fix: 15 bug fixes for v3.1.0 dashboard and Track E features

Bug fixes (ordered by priority):
- BUG-14 (P1): Fix ImportError in per-user MCP endpoint
- BUG-8 (P2): Raise clear error when PUBLIC_URL missing for OAuth
- BUG-12 (P3): Validate ENCRYPTION_KEY at startup
- BUG-13 (P4): Handle stale JWT gracefully on site creation
- BUG-11 (P5): Add auth validation to WordPress health checks
- BUG-15 (P6): Fix copy button showing Python repr (dict method shadow)
- BUG-1 (P7): Dynamic version from pyproject.toml instead of hardcoded
- BUG-5 (P8): Fix server mode default (sse → streamable-http)
- BUG-9 (P9): Plugin-specific example tools in endpoint instructions
- BUG-4 (P10): Fix settings page sidebar RBAC (session type mismatch)
- BUG-6 (P11): Show real plugin descriptions instead of 'No description'
- BUG-2 (P12): Remove stale 'phase: X.3' from system info
- BUG-10 (P13): Guard timestamps against None in Recent Activity
- BUG-3 (P14): Guard timestamps against None in audit logs
- BUG-7 (P15): Styled 404 page instead of plain text

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/user_auth.py

@@ -104,6 +104,12 @@ class UserAuth:
         self._registration_records: dict[str, list[float]] = {}
 
         providers = self.available_providers()
+        if providers and not self._public_url:
+            logger.warning(
+                "OAuth providers configured (%s) but PUBLIC_URL is not set. "
+                "OAuth login will fail until PUBLIC_URL is configured.",
+                providers,
+            )
         logger.info(
             "UserAuth initialized: providers=%s, session_expiry=%dh",
             providers,
@@ -139,6 +145,12 @@ class UserAuth:
         Raises:
             ValueError: If provider is unsupported or not configured.
         """
+        if not self._public_url:
+            raise ValueError(
+                "PUBLIC_URL environment variable must be set for OAuth login to work. "
+                "Example: PUBLIC_URL=https://mcp.example.com"
+            )
+
         state = secrets.token_hex(32)
         self._pending_states[state] = time.time()
         self._cleanup_expired_states()