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/Dockerfile

@@ -16,7 +16,7 @@ COPY pyproject.toml .
 RUN python -m venv /opt/venv
 ENV PATH="/opt/venv/bin:$PATH"
 COPY src/ ./src/
-RUN pip install --no-cache-dir --upgrade pip && \
+RUN pip install --no-cache-dir "pip>=25.3" && \
     pip install --no-cache-dir .
 
 # Production stage