Add CRUD abilities for all post types

[0xAmaan]

Summary

Implements standardized CRUD abilities for WordPress posts that work uniformly across all post types (built-in and custom), as requested in #84.

New abilities

Ability	Description
core/create-post	Create posts with title, content, excerpt, status
core/get-post	Retrieve a single post by ID
core/list-posts	List posts with pagination, filtering, and search
core/update-post	Partial updates to existing posts
core/delete-post	Soft delete (trash) or permanent deletion

Key features

• Works with all post types - Parameterized via post_type field
• Respects WordPress capabilities - Full permission callbacks using current_user_can()
• Input/output validation - JSON Schema for all abilities
• Proper error handling - Returns WP_Error with appropriate HTTP status codes
• REST API ready - All abilities exposed via show_in_rest: true
• Semantic annotations - readonly, destructive, idempotent hints for tooling

Test plan

• All existing tests pass
• New unit tests cover all 5 CRUD abilities
• Permission checks tested for different user roles (admin, editor, subscriber)
• Error handling tested for edge cases (nonexistent posts, invalid input)

Closes #84

[github-actions]

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Co-authored-by: 0xAmaan <0xamaan@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>

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[codecov]

Codecov Report

❌ Patch coverage is 22.07792% with 420 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.82%. Comparing base (1ebde3f) to head (c74389d).
⚠️ Report is 1 commits behind head on trunk.

Files with missing lines	Patch %	Lines
includes/abilities/wp-post-abilities.php	22.24%	416 Missing ⚠️
includes/bootstrap.php	0.00%	4 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##              trunk     #153       +/-   ##
=============================================
- Coverage     80.46%   64.82%   -15.64%     
  Complexity      178      178               
=============================================
  Files            20       21        +1     
  Lines          1474     2013      +539     
  Branches        120      120               
=============================================
+ Hits           1186     1305      +119     
- Misses          288      708      +420     

Flag	Coverage Δ
javascript	94.61% <ø> (ø)
unit	58.90% <22.07%> (-17.42%)	⬇️

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