feat: Browser-Matrix Stufe 1.a + 2 weitere GT-Findings + Plausibility-LLM-Härtung

Stage 1.a Browser-Matrix (Task #15) — Multi-Engine Scaffolding:
  - consent-tester/Dockerfile: firefox + webkit + Xvfb deps
  - playwright install chromium firefox webkit
  - services/browser_profiles.py: Registry mit DEFAULT_PROFILES
    (Chromium-Headed/Firefox-Headed/WebKit-Headed/Mobile-Safari) +
    EXTRA_PROFILES (Chrome-Channel, Edge, Brave)
  - services/multi_browser_scanner.py: run_matrix() orchestriert N
    parallele Scans + worst-of-Aggregation + 3 Sub-Scores
    (Pre-Consent 50%, Reject-Respekt 30%, Banner-Design 20%) +
    Hard-Fail-Cap auf <60% bei Pre-Consent/Reject-Verstoß
  - routes_matrix.py: POST /scan-matrix Endpoint (eigenes Modul,
    damit main.py unter 500 LOC bleibt)
  KNOWN: Stage 1.a-Shim ruft alle Profile auf demselben Chromium,
    echte Engine-Diversität in Stage 1.b (consent_scanner.py Param)

Coverage-Gap 3 (Task #17): 2/3 verbleibende GT-Lücken geschlossen:
  - B9 impressum_multi_entity_check (IMPRESSUM-001): erkennt
    USt-IdNr/HR/GF-Fehlen pro Entity bei multi-entity Impressen
    (Elli: USt-IdNr nur bei Elli Mobility, fehlt bei VW Group Charging)
  - B10 transfer_mechanism_check (TRANSFER-001): pro Non-EU-Vendor
    in cmp_vendors prüft DSE auf DPF/SCCs/BCRs/Einwilligung im
    ±400-char-Window. Findet Vendors ohne benannten Mechanismus.
  - TH-RETENTION-002 (AI-Datenkategorie-Differenzierung) bleibt
    semantisch-tief, vorgesehen für Specialist-Agents Task #18.

Plausibility-LLM Empty-Response-Härtung (Task #16):
  - BATCH_SIZE 8 → 4, EXCERPT 4000 → 1500 chars, TIMEOUT 60 → 45s
  - Single-retry mit halbierter Batch wenn LLM empty content
    zurückgibt — qwen3:30b-a3b rejektiert manchmal ≥6-Item-Prompts
    unter format='json'. Falls auch Half-Batch empty: log + skip.
  - Pipeline läuft jetzt nicht mehr 10min in Timeouts.

GT-Coverage Sprung: 10/13 → 11/13 (85%). 4/4 HIGH ✓, 5/6 MEDIUM ✓,
2/3 LOW ✓.

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

consent-tester/Dockerfile

@@ -8,6 +8,13 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libdrm2 libxkbcommon0 libxcomposite1 libxdamage1 libxfixes3 \
     libxrandr2 libgbm1 libpango-1.0-0 libcairo2 libasound2 \
     curl \
+    # Browser-matrix stage 1: Firefox + WebKit deps + Xvfb (headed runs)
+    xvfb \
+    libdbus-glib-1-2 libxt6 \
+    libwoff1 libvpx7 libevent-2.1-7 libopus0 libgstreamer-plugins-base1.0-0 \
+    libgstreamer-gl1.0-0 libgstreamer1.0-0 libwebpdemux2 libharfbuzz-icu0 \
+    libenchant-2-2 libsecret-1-0 libhyphen0 libmanette-0.2-0 libflite1 \
+    libgles2 libx264-164 \
     && rm -rf /var/lib/apt/lists/*
 
 # Create user BEFORE installing Playwright (so browsers are in user's cache)
@@ -17,8 +24,9 @@ COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 # Install Playwright browsers AS appuser (so they land in /home/appuser/.cache/)
+# Stage 1: chromium + firefox + webkit (Mobile-Safari = WebKit + devices preset)
 USER appuser
-RUN playwright install chromium
+RUN playwright install chromium firefox webkit
 USER root
 
 COPY . .