fix: reuse shared conditionsSchema for discussion conditions

Use z.lazy(() => conditionsSchema) instead of duplicating the array
schema inline, ensuring discussion conditions get the same
altTemplateContext support and error messages as element conditions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: JamesPHoughton

server/src/preFlight/validateTreatmentFile.ts

@@ -283,16 +283,7 @@ export const discussionSchema = z
     // New: allow discussion-level position-based visibility controls
     showToPositions: showToPositionsSchema.optional(),
     hideFromPositions: hideFromPositionsSchema.optional(),
-    conditions: z
-      .array(
-        z.lazy(() => conditionSchema),
-        {
-          invalid_type_error:
-            "Expected an array for `conditions`. Make sure each item starts with a dash (`-`) in YAML.",
-        }
-      )
-      .nonempty()
-      .optional(),
+    conditions: z.lazy(() => conditionsSchema).optional(),
   })
   .strict()
   .superRefine((data, ctx) => {