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/config.py

@@ -62,6 +62,7 @@ OPENAI_MODEL = os.environ.get("OPENAI_MODEL", "gpt-5.2")
 
 # ── Session config ──
 SESSION_MAX_AGE = int(os.environ.get("SESSION_MAX_AGE", 30 * 86400))  # 30 days
+SESSION_COOKIE_SECURE = os.environ.get("SESSION_COOKIE_SECURE", "").lower() in {"1", "true", "yes", "on"}
 DEV_AUTO_LOGIN = os.environ.get("DEV_AUTO_LOGIN", "").lower() in {"1", "true", "yes", "on"}
 DEV_AUTO_LOGIN_USERNAME = os.environ.get("DEV_AUTO_LOGIN_USERNAME", "dev")
 DEV_AUTO_LOGIN_DISPLAY_NAME = os.environ.get("DEV_AUTO_LOGIN_DISPLAY_NAME", "Dev User")