Add pagination to admin user list and validation annotations to all DTOs

- Implement server-side pagination in AdminService.getAllUsers() with search and filter support
- Update AdminController to accept page, pageSize, search, and filter query parameters
- Return Spring Data Page<> with total pages and paginated content
- Add validation annotations to 20+ request DTOs covering:
  - String length and format validation (@notblank, @SiZe, @pattern)
  - Numeric range validation (@min, @max)
  - Collection validation (@notempty)
  - Nested validation (@Valid)
- Change default admin credentials to email: admin, password: admin (configurable via env vars)

96 of 97 backend tests pass (1 contextLoads test requires DB setup)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: iii123iii

backend/src/main/java/com/crystalpdf/backend/controller/AdminController.java

@@ -10,7 +10,7 @@
 import org.springframework.security.core.annotation.AuthenticationPrincipal;
 import org.springframework.web.bind.annotation.*;
 
-import java.util.List;
+import org.springframework.data.domain.Page;
 import java.util.Map;
 
 @RestController
@@ -28,9 +28,14 @@ private void requireAdmin(User user) {
     }
 
     @GetMapping("/users")
-    public ResponseEntity<List<AdminUserResponse>> listUsers(@AuthenticationPrincipal User user) {
+    public ResponseEntity<Page<AdminUserResponse>> listUsers(
+            @RequestParam(defaultValue = "0") int page,
+            @RequestParam(defaultValue = "20") int pageSize,
+            @RequestParam(required = false) String search,
+            @RequestParam(required = false) String filter,
+            @AuthenticationPrincipal User user) {
         requireAdmin(user);
-        return ResponseEntity.ok(adminService.getAllUsers());
+        return ResponseEntity.ok(adminService.getAllUsers(page, pageSize, search, filter));
     }
 
     @PatchMapping("/users/{id}/storage-limit")

backend/src/main/java/com/crystalpdf/backend/dto/CompressRequest.java

@@ -1,3 +1,12 @@
 package com.crystalpdf.backend.dto;
 
-public record CompressRequest(String level, String sourcePassword) {}
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Pattern;
+
+public record CompressRequest(
+        @NotBlank(message = "Compression level is required")
+        @Pattern(regexp = "low|medium|high", message = "Level must be 'low', 'medium', or 'high'")
+        String level,
+
+        String sourcePassword
+) {}

backend/src/main/java/com/crystalpdf/backend/dto/CropRequest.java

@@ -1,17 +1,46 @@
 package com.crystalpdf.backend.dto;
 
+import jakarta.validation.Valid;
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotNull;
+
 import java.util.List;
 
 public record CropRequest(
         String sourcePassword,
         // Legacy: uniform margins applied to all pages (or pages list)
+        @Min(value = 0, message = "Top margin must be non-negative")
         Float marginTop,
+
+        @Min(value = 0, message = "Right margin must be non-negative")
         Float marginRight,
+
+        @Min(value = 0, message = "Bottom margin must be non-negative")
         Float marginBottom,
+
+        @Min(value = 0, message = "Left margin must be non-negative")
         Float marginLeft,
+
         List<Integer> pages,
+
         // Per-page: each entry specifies margins for a specific page
+        @Valid
         List<PageCropEntry> pageCrops
 ) {
-    public record PageCropEntry(int page, float marginTop, float marginRight, float marginBottom, float marginLeft) {}
+    public record PageCropEntry(
+            @NotNull(message = "Page number is required")
+            int page,
+
+            @Min(value = 0, message = "Top margin must be non-negative")
+            float marginTop,
+
+            @Min(value = 0, message = "Right margin must be non-negative")
+            float marginRight,
+
+            @Min(value = 0, message = "Bottom margin must be non-negative")
+            float marginBottom,
+
+            @Min(value = 0, message = "Left margin must be non-negative")
+            float marginLeft
+    ) {}
 }

backend/src/main/java/com/crystalpdf/backend/dto/DeleteAccountRequest.java

@@ -1,3 +1,8 @@
 package com.crystalpdf.backend.dto;
 
-public record DeleteAccountRequest(String password) {}
+import jakarta.validation.constraints.NotBlank;
+
+public record DeleteAccountRequest(
+        @NotBlank(message = "Password is required")
+        String password
+) {}

backend/src/main/java/com/crystalpdf/backend/dto/DeletePagesRequest.java

@@ -1,5 +1,12 @@
 package com.crystalpdf.backend.dto;
 
+import jakarta.validation.constraints.NotEmpty;
+
 import java.util.List;
 
-public record DeletePagesRequest(List<Integer> pages, String sourcePassword) {}
+public record DeletePagesRequest(
+        @NotEmpty(message = "Pages list is required")
+        List<Integer> pages,
+
+        String sourcePassword
+) {}

backend/src/main/java/com/crystalpdf/backend/dto/ExtractImagesRequest.java

@@ -1,6 +1,12 @@
 package com.crystalpdf.backend.dto;
 
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Pattern;
+
 public record ExtractImagesRequest(
         String sourcePassword,
+
+        @NotBlank(message = "Image format is required")
+        @Pattern(regexp = "png|jpg|jpeg", message = "Format must be 'png', 'jpg', or 'jpeg'")
         String format
 ) {}

backend/src/main/java/com/crystalpdf/backend/dto/ExtractSelectionRequest.java

@@ -1,5 +1,12 @@
 package com.crystalpdf.backend.dto;
 
+import jakarta.validation.constraints.NotEmpty;
+
 import java.util.List;
 
-public record ExtractSelectionRequest(List<Integer> pages, String sourcePassword) {}
+public record ExtractSelectionRequest(
+        @NotEmpty(message = "Pages list is required")
+        List<Integer> pages,
+
+        String sourcePassword
+) {}

backend/src/main/java/com/crystalpdf/backend/dto/FlattenAnnotationsRequest.java

@@ -1,11 +1,22 @@
 package com.crystalpdf.backend.dto;
 
+import jakarta.validation.Valid;
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotEmpty;
+import jakarta.validation.constraints.NotNull;
+
 import java.util.List;
 import java.util.Map;
 
 public record FlattenAnnotationsRequest(
+        @NotEmpty(message = "Pages map is required")
+        @Valid
         Map<Integer, FlattenAnnotationsRequest.PageData> pages,
+
+        @Min(value = 0, message = "Scale must be positive")
         double scale,
+
         String sourcePassword
 ) {
     public record PageData(
@@ -14,20 +25,42 @@ public record PageData(
     ) {}
 
     public record StrokeData(
+            @NotBlank(message = "Stroke type is required")
             String type,
+
+            @NotBlank(message = "Stroke color is required")
             String color,
+
+            @Min(value = 0, message = "Width must be non-negative")
             double width,
+
+            @Min(value = 0, message = "Opacity must be non-negative")
             double opacity,
+
+            @NotEmpty(message = "Stroke points are required")
             List<List<Double>> points
     ) {}
 
     public record TextData(
+            @NotBlank(message = "Text ID is required")
             String id,
+
+            @Min(value = 0, message = "X must be non-negative")
             double x,
+
+            @Min(value = 0, message = "Y must be non-negative")
             double y,
+
+            @Min(value = 0, message = "Width must be non-negative")
             double width,
+
+            @Min(value = 0, message = "Font size must be positive")
             double fontSize,
+
+            @NotBlank(message = "Text color is required")
             String color,
+
+            @NotBlank(message = "Text content is required")
             String text
     ) {}
 }

backend/src/main/java/com/crystalpdf/backend/dto/HeaderFooterRequest.java

@@ -1,5 +1,8 @@
 package com.crystalpdf.backend.dto;
 
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotNull;
+
 public record HeaderFooterRequest(
         String sourcePassword,
         String headerLeft,
@@ -8,5 +11,8 @@ public record HeaderFooterRequest(
         String footerLeft,
         String footerCenter,
         String footerRight,
+
+        @NotNull(message = "Font size is required")
+        @Min(value = 6, message = "Font size must be at least 6")
         Float fontSize
 ) {}

backend/src/main/java/com/crystalpdf/backend/dto/MergeRequest.java

@@ -1,5 +1,12 @@
 package com.crystalpdf.backend.dto;
 
+import jakarta.validation.constraints.NotEmpty;
+
 import java.util.List;
 
-public record MergeRequest(List<Long> otherDocumentIds, String sourcePassword) {}
+public record MergeRequest(
+        @NotEmpty(message = "At least one document to merge is required")
+        List<Long> otherDocumentIds,
+
+        String sourcePassword
+) {}