fix(#365): fix ruff, mypy, pip, and bandit issues in coordinator

- Fix 20 ruff errors: UP035 (Callable import), UP042 (StrEnum), E501
  (line length), F401 (unused imports), UP045 (Optional -> X | None),
  I001 (import sorting)
- Fix mypy error: wrap slowapi rate limit handler with
  Exception-compatible signature for add_exception_handler
- Pin pip >= 25.3 in Dockerfile (CVE-2025-8869, CVE-2026-1703)
- Add nosec B104 to config.py (container-bound 0.0.0.0 is acceptable)
- Add nosec B101 to telemetry.py (assert for type narrowing)
- Create bandit.yaml to suppress B404/B607/B603 in gates/ tooling

Fixes #365

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

apps/coordinator/src/circuit_breaker.py

@@ -13,13 +13,14 @@ Reference: SEC-ORCH-7 from security review
 
 import logging
 import time
-from enum import Enum
-from typing import Any, Callable
+from collections.abc import Callable
+from enum import StrEnum
+from typing import Any
 
 logger = logging.getLogger(__name__)
 
 
-class CircuitState(str, Enum):
+class CircuitState(StrEnum):
     """States for the circuit breaker."""
 
     CLOSED = "closed"  # Normal operation