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.

tests/unit/test_metadata.py

@@ -0,0 +1,134 @@
+"""Tests for metadata endpoint."""
+import json
+
+import pytest
+from fastapi.testclient import TestClient
+
+
+class TestMetadataEndpoint:
+    """Tests for OAuth 2.0 Authorization Server Metadata endpoint."""
+
+    @pytest.fixture
+    def client(self, monkeypatch):
+        """Create test client with valid configuration."""
+        monkeypatch.setenv("GONDULF_SECRET_KEY", "test-secret-key-must-be-at-least-32-chars-long")
+        monkeypatch.setenv("GONDULF_BASE_URL", "https://auth.example.com")
+
+        # Import app AFTER setting env vars
+        from gondulf.main import app
+
+        return TestClient(app)
+
+    def test_metadata_endpoint_returns_200(self, client):
+        """Test metadata endpoint returns 200 OK."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        assert response.status_code == 200
+
+    def test_metadata_content_type_json(self, client):
+        """Test metadata endpoint returns JSON content type."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        assert response.headers["content-type"] == "application/json"
+
+    def test_metadata_cache_control_header(self, client):
+        """Test metadata endpoint sets Cache-Control header."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        assert "cache-control" in response.headers
+        assert "public" in response.headers["cache-control"]
+        assert "max-age=86400" in response.headers["cache-control"]
+
+    def test_metadata_all_required_fields_present(self, client):
+        """Test metadata response contains all required fields."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        required_fields = [
+            "issuer",
+            "authorization_endpoint",
+            "token_endpoint",
+            "response_types_supported",
+            "grant_types_supported",
+            "code_challenge_methods_supported",
+            "token_endpoint_auth_methods_supported",
+            "revocation_endpoint_auth_methods_supported",
+            "scopes_supported"
+        ]
+
+        for field in required_fields:
+            assert field in data, f"Missing required field: {field}"
+
+    def test_metadata_issuer_matches_base_url(self, client):
+        """Test issuer field matches BASE_URL configuration."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["issuer"] == "https://auth.example.com"
+
+    def test_metadata_authorization_endpoint_correct(self, client):
+        """Test authorization_endpoint field is correct."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["authorization_endpoint"] == "https://auth.example.com/authorize"
+
+    def test_metadata_token_endpoint_correct(self, client):
+        """Test token_endpoint field is correct."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["token_endpoint"] == "https://auth.example.com/token"
+
+    def test_metadata_response_types_supported(self, client):
+        """Test response_types_supported contains only 'code'."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["response_types_supported"] == ["code"]
+
+    def test_metadata_grant_types_supported(self, client):
+        """Test grant_types_supported contains only 'authorization_code'."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["grant_types_supported"] == ["authorization_code"]
+
+    def test_metadata_code_challenge_methods_empty(self, client):
+        """Test code_challenge_methods_supported is empty array."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["code_challenge_methods_supported"] == []
+
+    def test_metadata_token_endpoint_auth_methods(self, client):
+        """Test token_endpoint_auth_methods_supported contains 'none'."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["token_endpoint_auth_methods_supported"] == ["none"]
+
+    def test_metadata_revocation_endpoint_auth_methods(self, client):
+        """Test revocation_endpoint_auth_methods_supported contains 'none'."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["revocation_endpoint_auth_methods_supported"] == ["none"]
+
+    def test_metadata_scopes_supported_empty(self, client):
+        """Test scopes_supported is empty array."""
+        response = client.get("/.well-known/oauth-authorization-server")
+        data = response.json()
+
+        assert data["scopes_supported"] == []
+
+    def test_metadata_response_valid_json(self, client):
+        """Test metadata response can be parsed as valid JSON."""
+        response = client.get("/.well-known/oauth-authorization-server")
+
+        # Should not raise exception
+        data = json.loads(response.content)
+        assert isinstance(data, dict)
+
+    def test_metadata_endpoint_no_authentication_required(self, client):
+        """Test metadata endpoint is accessible without authentication."""
+        # No authentication headers
+        response = client.get("/.well-known/oauth-authorization-server")
+        assert response.status_code == 200