security: address all findings from vulnerability assessment

Implements the fixes catalogued under Task Master tasks 1-19, derived
from the security audit at .claude/plans/adaptive-sleeping-diffie.md.

Critical
- C-1 SSRF userinfo bypass: PDF proxy now rejects URLs containing
  userinfo or non-default ports, and asserts netloc == hostname.
- C-2 No authentication: optional NADLAN_API_KEY gate guards
  /api/search/*, /api/appraisals/pdf and /mcp until Traefik mTLS
  is wired up. Default behavior unchanged when env unset.

High
- H-1 Error info leak: HTTPException details replaced with generic
  string; full exceptions still logged via logger.exception.
- H-2 Security headers middleware: HSTS, X-Frame-Options, nosniff,
  Referrer-Policy, Permissions-Policy, CSP, server-banner stripped.
- H-3 Swagger gated: /api/docs and /api/openapi.json hidden when
  ENVIRONMENT=production.
- H-4 PDF proxy DoS: streams in 8KB chunks, rejects upstream above
  50MB Content-Length, also rejects mid-stream overrun. Magic-byte
  check moved before StreamingResponse so we can 502 cleanly.
- H-5 Per-IP rate limit: token-bucket per (path, IP) on /mcp,
  /api/search/*, /api/appraisals/pdf. Reads X-Forwarded-For for
  client IP behind Traefik.

Medium
- M-1 CORS: ALLOWED_ORIGINS env, allow_headers narrowed, no creds.
- M-2 Deal model: extra="ignore" + explicit fields for gushNum,
  parcelNum, subParcelNum, streetNameHeb, houseNum, deal_source,
  deal_type, deal_type_description, distance_meters. Frontend now
  reads snake_case.
- M-3 Input validators: regex on block, plot, appraiser names,
  dates, address, free-text — Hebrew + Latin + safe punctuation.
- M-4 COOLIFY_UUID moved out of deploy.yaml into Gitea Actions
  secret.
- M-5 Base images pinned to sha256 digests.
- M-6 Runtime deps tightened to ~= compatible-release.
- M-7 1MB request-body size limit middleware.

Low / privacy
- L-1 Heebo self-hosted via @fontsource. Removed Google Fonts links
  and CSP entries. Added meta referrer + meta robots noindex.
- L-2 Cache-Control: immutable for /assets, no-cache for HTML.
- L-3 Logger no longer prints user-supplied addresses; emits length
  only.
- L-4 Dockerfile healthcheck uses literal port 8000.
- L-5 PDF proxy stream cleanup uses contextlib.suppress.

Tests: 331 passed, 17 skipped. Frontend typecheck passes.
Findings file: .claude/plans/adaptive-sleeping-diffie.md
Tasks: .taskmaster/tasks/tasks.json

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -1,5 +1,7 @@
 # ─── Stage 1: build the React UI ────────────────────────────────────────
-FROM node:22-alpine AS web-build
+# Pinned to digest to neutralize tag-hijack and supply-chain replay.
+# Renovate/dependabot can update this digest periodically.
+FROM node:22-alpine@sha256:8ea2348b068a9544dae7317b4f3aafcdc032df1647bb7d768a05a5cad1a7683f AS web-build
 WORKDIR /web
 
 # Cache deps separately from sources.
@@ -10,7 +12,7 @@ COPY web/ .
 RUN npm run build
 
 # ─── Stage 2: Python runtime ────────────────────────────────────────────
-FROM python:3.13-slim
+FROM python:3.13-slim@sha256:a0779d7c12fc20be6ec6b4ddc901a4fd7657b8a6bc9def9d3fde89ed5efe0a3d
 
 ENV PYTHONUNBUFFERED=1 \
     PYTHONDONTWRITEBYTECODE=1 \
@@ -43,6 +45,6 @@ USER appuser
 EXPOSE 8000
 
 HEALTHCHECK --interval=30s --timeout=10s --start-period=15s --retries=3 \
-    CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:${PORT:-8000}/health')" || exit 1
+    CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/health')" || exit 1
 
 CMD ["python", "run_http_server.py"]