feat(phase-2): implement domain verification system

Implements complete domain verification flow with:
- rel=me link verification service
- HTML fetching with security controls
- Rate limiting to prevent abuse
- Email validation utilities
- Authorization and verification API endpoints
- User-facing templates for authorization and verification flows

This completes Phase 2: Domain Verification as designed.

Tests:
- All Phase 2 unit tests passing
- Coverage: 85% overall
- Migration tests updated

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

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

pyproject.toml

@@ -29,6 +29,8 @@ dependencies = [
     "python-dotenv>=1.0.0",
     "dnspython>=2.4.0",
     "aiosmtplib>=3.0.0",
+    "beautifulsoup4>=4.12.0",
+    "jinja2>=3.1.0",
 ]
 
 [project.optional-dependencies]