style: clean up markdownlint config

Sort rules alphabetically and remove obsolete ignore patterns.

Signed-off-by: umatare5 <umatare5@gmail.com>
AI-assisted-by: GitHub Copilot Coding Agent

Author: umatare5

.markdownlint-cli2.jsonc

@@ -1,24 +1,22 @@
 {
   "config": {
     "default": true,
-    "line_length": false,
-    "no-inline-html": false,
-    "no-trailing-punctuation": false,
-    "no-duplicate-heading": false,
-    "no-bare-urls": false,
+    "first-line-h1": false,
     "header-increment": false,
+    "line_length": false,
     "no-alt-text": false,
+    "no-bare-urls": false,
     "no-blanks-blockquote": false,
+    "no-duplicate-heading": false,
+    "no-inline-html": false,
+    "no-trailing-punctuation": false,
   },
   "ignores": [
     "vendor/**",
-    ".copilot_reports/**",
     ".github/instructions/**",
     ".github/copilot-instructions.md",
     ".claude/CLAUDE.md",
     ".gemini/GEMINI.md",
-    "README.md",
-    ".github/prompts/**/*.prompt.md",
   ],
   "globs": ["**/*.md"],
 }