docs: update comprehensive API documentation and project guides

This commit updates all documentation files throughout the project:

- Updated IMPLEMENTATION_PLAN.md with new implementation details
- Updated PROJECT_GUIDELINES.md with coding standards and practices
- Updated README.md with current project information
- Updated SCREENSHOT_AUTOMATION.md with new automation details
- Added TEST_DATA.md with test fixtures data
- Updated cover_image_serving_plan.md with static URL patterns

Documentation API updates:
- Updated API reference documentation for all endpoints including:
  - Authentication (login, logout, register, refresh_token)
  - Book matching (auto_link, bulk_link, link_book, search)
  - Collections (CRUD operations, shelf mappings, auto-assign rules)
  - Conflicts (bulk operations, resolve/dismiss)
  - Devices (registration, approval, shelf management)
  - Highlights (create, update, delete, get)
  - Kobo sync (bookmark, markup, initialization, sync)
  - KOReader sync (library, metadata, bookmarks, progress)
  - Libraries (CRUD, folders, media items, stats)
  - Media items (bulk operations, CRUD)
  - Notes (CRUD operations)
  - OPDS (acquisition, feeds, publication)
  - Progress (reading progress tracking)
  - Queue (device queue management)
  - Ratings (star ratings)
  - Scanner (watch mode, scan operations)
  - Sync protocols (Kobo, KOReader)
  - Users (profile, password, admin operations)
  - WebSocket protocols

- Updated user guides (admin, dashboard, settings, sync)
- Updated device setup guides (Kobo, KOReader)
- Updated developer guides (testing, contributing, operations)
- Updated scripts/README.md

docs/developer/api/users/delete_user.md

@@ -3,6 +3,7 @@
 Delete a user account. Supports both self-deletion and admin deletion.
 
 **Endpoints**:
+
 - Self-deletion: `DELETE /api/auth/profile`
 - Admin deletion: `DELETE /api/auth/profile/:id`
 
@@ -32,12 +33,12 @@ Admins can delete any user account by providing the user ID in the URL.
 
 ## Error Responses
 
-| Code | Description |
-|------|-------------|
-| 400 | Cannot delete the last admin |
-| 401 | Invalid or expired token |
-| 403 | Admin access required (trying to delete another user) |
-| 404 | User not found (admin mode only) |
+| Code | Description                                           |
+| ---- | ----------------------------------------------------- |
+| 400  | Cannot delete the last admin                          |
+| 401  | Invalid or expired token                              |
+| 403  | Admin access required (trying to delete another user) |
+| 404  | User not found (admin mode only)                      |
 
 ## Safety Rules