Implements Alpha post creation feature with full write-forward to community
PDS and real-time Jetstream indexing.

Features:
- POST /xrpc/social.coves.post.create endpoint
- Write-forward architecture (posts written to community's PDS repository)
- Real-time AppView indexing via Jetstream consumer
- Comprehensive security validation (auth, repository ownership, FK integrity)
- Support for all 4 at-identifier formats (DIDs, canonical, @-prefixed, scoped)
- Database schema with proper indexing (migration 011)
- Full integration test suite (service, repository, handler, E2E with live PDS)

Implementation:
- Domain layer: Post models, service, validation
- Repository layer: PostgreSQL with JSON support
- Handler layer: XRPC endpoint with OAuth auth
- Consumer layer: Jetstream real-time indexing with security checks
- 13 commits, 30+ files, ~2,700 lines

Deferred to Beta:
- Content rules validation
- Post read operations (get, list)
- Post update/delete operations
- Voting system

See docs/PRD_POSTS.md for complete status.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Update lexicon validation tests to handle post record types:
- Add social.coves.post.record to test cases
- Verify at-identifier format for community field
- Validate author field (required DID)

Ensures lexicon validation works correctly for new post records.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Move duplicate helper functions from multiple test files to helpers.go:
- authenticateWithPDS() - Used by post e2e tests
- contains() / anySubstring() - String utilities
- Import standardization across test files

Benefits:
- Eliminates code duplication across 6+ test files
- Centralizes test utilities for easier maintenance
- Improves test readability (focus on test logic, not helpers)

All tests continue to pass with consolidated helpers.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Minor formatting cleanup:
- Align struct field comments consistently
- No functional changes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Add SetTestUserDID() function to inject user DID into context for testing.

Purpose:
- Mock authenticated users in integration tests without full OAuth flow
- Used by post handler tests to simulate authenticated requests
- Marked with comment: "ONLY be used in tests"

This enables testing authenticated endpoints (like post creation)
without requiring real PDS authentication in test environment.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Update PRD_POSTS.md with implementation status:
- Add "Implementation Status" section showing completed work
- Mark Alpha CREATE features as complete (✅)
- Mark Beta features as deferred (⚠️)
- Update all sections with checkmarks and status
- Add database schema status (migration 011 complete)
- Update success metrics (Alpha checklist complete)
- Reference IMPLEMENTATION_POST_CREATION.md for details

Completed (Alpha):
✅ Post creation endpoint with write-forward to community PDS
✅ Handler with authentication, validation, security checks
✅ Service layer with token refresh and community resolution
✅ PostgreSQL repository with proper indexing
✅ Jetstream consumer for real-time indexing
✅ E2E tests (service, repository, handler, live PDS+Jetstream)
✅ All 4 at-identifier formats supported

Deferred (Beta):
⚠️ Content rules validation
⚠️ Post read operations (get, list)
⚠️ Post update/edit operations
⚠️ Post deletion
⚠️ Voting system

Update other PRDs:
- PRD_BACKLOG: Add post creation to completed items
- PRD_COMMUNITIES: Reference post integration
- PRD_GOVERNANCE: Note content rules deferred to Beta

PRDs now accurately reflect codebase state.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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