chore(F.15): FastMCP 3.x upgrade + legacy cleanup — v3.5.0

- Upgrade fastmcp from >=2.14.0,<3.0.0 to >=3.0.0,<4.0.0
- Remove server_multi.py (legacy multi-endpoint server)
- Remove core/project_manager.py (legacy project manager)
- Refactor HealthMonitor to use SiteManager exclusively
- Replace _tool_manager._tools with tracked _tool_counts dict
- Clean core/__init__.py exports
- Update CHANGELOG, CLAUDE.md, tests
- Auto-format fixes (black + ruff)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/legacy/test_health_monitor.py

@@ -24,7 +24,7 @@ if sys.platform == "win32":
 # Add project root to path
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 
-from core import AuditLogger, ProjectManager, initialize_health_monitor
+from core import AuditLogger, initialize_health_monitor
 
 
 async def test_health_monitor():
@@ -35,11 +35,9 @@ async def test_health_monitor():
 
     # Initialize components
     print("\n1. Initializing components...")
-    project_manager = ProjectManager()
     audit_logger = AuditLogger()
 
     health_monitor = initialize_health_monitor(
-        project_manager=project_manager,
         audit_logger=audit_logger,
         metrics_retention_hours=24,
         max_metrics_per_project=1000,