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/responses.py

@@ -5,7 +5,7 @@ Platform Gateway — Response helpers mixed into GatewayHandler.
 import json
 from http.cookies import SimpleCookie
 
-from config import SESSION_MAX_AGE, DEV_AUTO_LOGIN
+from config import SESSION_MAX_AGE, SESSION_COOKIE_SECURE, DEV_AUTO_LOGIN
 from sessions import get_session_user, get_or_create_dev_user
 
 
@@ -43,8 +43,10 @@ class ResponseMixin:
         return user
 
     def _set_session_cookie(self, token):
-        self.send_header("Set-Cookie",
-                         f"platform_session={token}; Path=/; HttpOnly; Secure; SameSite=Lax; Max-Age={SESSION_MAX_AGE}")
+        cookie = f"platform_session={token}; Path=/; HttpOnly; SameSite=Lax; Max-Age={SESSION_MAX_AGE}"
+        if SESSION_COOKIE_SECURE:
+            cookie += "; Secure"
+        self.send_header("Set-Cookie", cookie)
 
     def _read_body(self):
         length = int(self.headers.get("Content-Length", 0))