Refactor gateway into modular architecture

Split 1878-line server.py into 15 focused modules:
- config.py: all env vars and constants
- database.py: schema, init, seed logic
- sessions.py: session/token CRUD
- proxy.py: proxy_request, SERVICE_MAP, resolve_service
- responses.py: ResponseMixin for handler helpers
- auth.py: login/logout/register handlers
- dashboard.py: dashboard, apps, connections, pinning
- command.py: AI command bar
- integrations/booklore.py: auth, books, cover, import
- integrations/kindle.py: send-to-kindle, file finder
- integrations/karakeep.py: save/delete bookmarks
- integrations/qbittorrent.py: download status
- integrations/image_proxy.py: external image proxy

server.py is now thin routing only (~344 lines).
All routes, methods, status codes, and responses preserved exactly.
Added PYTHONUNBUFFERED=1 to Dockerfile for live logging.

gateway/integrations/image_proxy.py

@@ -0,0 +1,36 @@
+"""
+Platform Gateway — Image proxy (bypass hotlink protection).
+"""
+
+import urllib.request
+import urllib.parse
+
+from config import _ssl_ctx
+
+
+def handle_image_proxy(handler):
+    """Proxy external images to bypass hotlink protection (e.g. Reddit)."""
+    qs = urllib.parse.urlparse(handler.path).query
+    params = urllib.parse.parse_qs(qs)
+    url = params.get("url", [None])[0]
+    if not url:
+        handler._send_json({"error": "Missing url parameter"}, 400)
+        return
+    try:
+        req = urllib.request.Request(url, headers={
+            "User-Agent": "Mozilla/5.0 (compatible; PlatformProxy/1.0)",
+            "Accept": "image/*,*/*",
+            "Referer": urllib.parse.urlparse(url).scheme + "://" + urllib.parse.urlparse(url).netloc + "/",
+        })
+        resp = urllib.request.urlopen(req, timeout=10, context=_ssl_ctx)
+        body = resp.read()
+        ct = resp.headers.get("Content-Type", "image/jpeg")
+        handler.send_response(200)
+        handler.send_header("Content-Type", ct)
+        handler.send_header("Content-Length", len(body))
+        handler.send_header("Cache-Control", "public, max-age=86400")
+        handler.end_headers()
+        handler.wfile.write(body)
+    except Exception as e:
+        print(f"[ImageProxy] Error fetching {url}: {e}")
+        handler._send_json({"error": "Failed to fetch image"}, 502)