[AZ-178] Fix Critical/High security findings: auth, CVEs, non-root containers, per-job SSE

- Pin all deps; h11==0.16.0 (CVE-2025-43859), python-multipart>=1.3.1 (CVE-2026-28356), PyJWT==2.12.1
- Add HMAC JWT verification (require_auth FastAPI dependency, JWT_SECRET-gated)
- Fix TokenManager._refresh() to use ADMIN_API_URL instead of ANNOTATIONS_URL
- Rename POST /detect → POST /detect/image (image-only, rejects video files)
- Replace global SSE stream with per-job SSE: GET /detect/{media_id} with event replay buffer
- Apply require_auth to all 4 protected endpoints
- Fix on_annotation/on_status closure to use mutable current_id for correct post-upload event routing
- Add non-root appuser to Dockerfile and Dockerfile.gpu
- Add JWT_SECRET to e2e/docker-compose.test.yml and run-tests.sh
- Update all e2e tests and unit tests for new endpoints and HMAC token signing
- 64/64 tests pass

Made-with: Cursor

Dockerfile.gpu

@@ -6,5 +6,8 @@ RUN pip3 install --no-cache-dir -r requirements-gpu.txt
 COPY . .
 RUN python3 setup.py build_ext --inplace
 ENV PYTHONPATH=/app/src
+RUN adduser --disabled-password --no-create-home --gecos "" appuser \
+    && chown -R appuser /app
+USER appuser
 EXPOSE 8080
 CMD ["python3", "-m", "uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8080"]