feat(phase-4a): complete Phase 3 implementation and gap analysis

Merges Phase 4a work including:

Implementation:
- Metadata discovery endpoint (/api/.well-known/oauth-authorization-server)
- h-app microformat parser service
- Enhanced authorization endpoint with client info display
- Configuration management system
- Dependency injection framework

Documentation:
- Comprehensive gap analysis for v1.0.0 compliance
- Phase 4a clarifications on development approach
- Phase 4-5 critical components breakdown

Testing:
- Unit tests for h-app parser (308 lines, comprehensive coverage)
- Unit tests for metadata endpoint (134 lines)
- Unit tests for configuration system (18 lines)
- Integration test updates

All tests passing with high coverage. Ready for Phase 4b security hardening.

src/gondulf/dependencies.py

@@ -6,6 +6,7 @@ from gondulf.database.connection import Database
 from gondulf.dns import DNSService
 from gondulf.email import EmailService
 from gondulf.services.domain_verification import DomainVerificationService
+from gondulf.services.happ_parser import HAppParser
 from gondulf.services.html_fetcher import HTMLFetcherService
 from gondulf.services.rate_limiter import RateLimiter
 from gondulf.services.relme_parser import RelMeParser
@@ -70,6 +71,12 @@ def get_relme_parser() -> RelMeParser:
     return RelMeParser()
 
 
+@lru_cache
+def get_happ_parser() -> HAppParser:
+    """Get singleton h-app parser service."""
+    return HAppParser(html_fetcher=get_html_fetcher())
+
+
 @lru_cache
 def get_rate_limiter() -> RateLimiter:
     """Get singleton rate limiter service."""