Add POST /xrpc/social.coves.post.create endpoint:
- Authentication required via OAuth middleware
- Validate request body size (1MB limit for DoS prevention)
- Validate at-identifier format for community field
- Reject client-provided authorDid (security)
- Set authorDid from authenticated JWT
- Error mapping for lexicon-compliant responses

Handler security features:
- Body size limit prevents DoS
- Author impersonation prevented
- All 4 at-identifier formats supported
- Proper error codes (400, 401, 403, 404, 500)

Route registration integrates with auth middleware.

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

- Add migration 011: posts table with indexes
- Add foreign keys to users and communities
- Add indexes for common query patterns (community feed, author, score)
- Add PostgreSQL repository implementation
- Add Create() and GetByURI() methods
- Add JSON serialization for facets, embeds, labels

Posts table supports:
- AT-URI, CID, rkey for atProto compliance
- Title, content, facets, embed, labels
- Vote counts and score (denormalized for performance)
- Soft delete with deleted_at timestamp

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

- Add Post domain model with AppView database representation
- Add CreatePostRequest/Response for XRPC endpoint
- Add PostRecord for PDS write-forward
- Add Service and Repository interfaces
- Add error types (ValidationError, ContentRuleViolation)
- Add service implementation with PDS write-forward
- Add validation for content length, labels, at-identifiers

Part of Alpha post creation feature.

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

Complete implementation of community handle naming convention change
with comprehensive PR review fixes.

This merge includes:
- Critical bug fixes for identifier resolution
- Comprehensive test coverage (31 test cases, all passing)
- Database migration for .communities → .community transition
- Input validation and error handling improvements
- Support for self-hosted instances

All PR review comments addressed:
✅ GetDisplayHandle() bug fixed for multi-part domains
✅ Case sensitivity bug fixed in resolveScopedIdentifier
✅ Comprehensive input validation (DNS labels, domain format)
✅ 100% test coverage for new code
✅ Database migration script with rollback
✅ Improved error messages with identifier context
✅ NewPDSAccountProvisioner argument order corrected
✅ Removed hardcoded coves.social from tests

Test Results:
- 31 identifier resolution tests: PASS
- All integration tests: PASS
- E2E tests with real PDS: PASS
- Regression tests: PASS

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

Update development environment configuration and Go module dependencies.

Changes:
- Update .env.dev with latest environment variables
- Update docker-compose.dev.yml configuration
- Run go mod tidy to clean up dependencies

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

Update Product Requirements Document to document the singular
.community. naming convention.

Changes:
- Update handle format examples
- Document identifier resolution features
- Update API examples with new handle format

This ensures documentation matches the implemented handle format
and provides clear examples for developers.

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