security: pip-audit + bandit gates that can fail; patch 29 known CVEs

security.yml previously ran safety/bandit/semgrep with `|| true` and could
not go red. Now: pip-audit on requirements.txt is a hard gate (dev deps
reported only), bandit HIGH fails (B104 bind-all skipped: intended behind
Cloudflare/Caddy), pip-licenses uploaded as a report. Weekly + on
dependency/source changes.

Running it locally found 29 advisories, all in pinned-and-forgotten
runtime deps: starlette 0.27 (7, incl. Host-header path confusion and
form DoS), fastapi 0.104, requests 2.31 (3), pymysql 1.1. Bumped to
current: fastapi 0.141.1 / starlette 1.6.0, pydantic 2.13.5, uvicorn
0.52.4, requests 2.34.2, pymysql 1.2.0; dev: pytest 9.1.1, black 26.5.1.
pip-audit is now clean. requires-python narrowed to 3.11 (the truth:
psycopg2-binary 2.9.9 fails on 3.13; pandas 2.0.3 has no 3.12 wheels).
Full suite passes; API smoke-tested (health, stations, forecast, history,
stats, docs, openapi) on the new stack. black 26 reformatted 8 files.

.gitea/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
       - name: Install tools
         run: |
           python -m pip install --upgrade pip --root-user-action=ignore
-          pip install --root-user-action=ignore black==23.11.0 isort==5.12.0 flake8==6.1.0
+          pip install --root-user-action=ignore black==26.5.1 isort==5.12.0 flake8==6.1.0
 
       - name: black
         run: black --check --diff src/ *.py
@@ -67,7 +67,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip --root-user-action=ignore
           pip install --root-user-action=ignore -r requirements.txt
-          pip install --root-user-action=ignore pytest==7.4.3 pytest-asyncio==0.21.1
+          pip install --root-user-action=ignore pytest==9.1.1 pytest-asyncio==0.21.1
 
       - name: pytest
         env: