feat: instant feedback button — creates Gitea issues with auto-labels

iOS:
- Subtle floating feedback button (bottom-left, speech bubble icon)
- Quick sheet: type → send → auto-creates Gitea issue
- Shows checkmark on success, auto-dismisses
- No friction — tap, type, done

Gateway:
- POST /api/feedback endpoint
- Auto-labels: bug/feature/enhancement + ios/web + fitness/brain/reader/podcasts
- Keyword detection for label assignment
- Creates issue via Gitea API with user name and source

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

gateway/Dockerfile

@@ -3,7 +3,7 @@ WORKDIR /app
 RUN pip install --no-cache-dir bcrypt
 RUN adduser --disabled-password --no-create-home appuser
 RUN mkdir -p /app/data && chown -R appuser /app/data
-COPY --chown=appuser server.py config.py database.py sessions.py proxy.py responses.py auth.py dashboard.py command.py assistant.py ./
+COPY --chown=appuser server.py config.py database.py sessions.py proxy.py responses.py auth.py dashboard.py command.py assistant.py feedback.py ./
 COPY --chown=appuser integrations/ ./integrations/
 EXPOSE 8100
 ENV PYTHONUNBUFFERED=1