feat: major platform expansion — Brain service, RSS reader, iOS app, AI assistants, Firefox extension

Brain Service:
- Playwright stealth crawler replacing browserless (og:image, Readability, Reddit JSON API)
- AI classification with tag definitions and folder assignment
- YouTube video download via yt-dlp
- Karakeep migration complete (96 items)
- Taxonomy management (folders with icons/colors, tags)
- Discovery shuffle, sort options, search (Meilisearch + pgvector)
- Item tag/folder editing, card color accents

RSS Reader Service:
- Custom FastAPI reader replacing Miniflux
- Feed management (add/delete/refresh), category support
- Full article extraction via Readability
- Background content fetching for new entries
- Mark all read with confirmation
- Infinite scroll, retention cleanup (30/60 day)
- 17 feeds migrated from Miniflux

iOS App (SwiftUI):
- Native iOS 17+ app with @Observable architecture
- Cookie-based auth, configurable gateway URL
- Dashboard with custom background photo + frosted glass widgets
- Full fitness module (today/templates/goals/food library)
- AI assistant chat (fitness + brain, raw JSON state management)
- 120fps ProMotion support

AI Assistants (Gateway):
- Unified dispatcher with fitness/brain domain detection
- Fitness: natural language food logging, photo analysis, multi-item splitting
- Brain: save/append/update/delete notes, search & answer, undo support
- Madiha user gets fitness-only (brain disabled)

Firefox Extension:
- One-click save to Brain from any page
- Login with platform credentials
- Right-click context menu (save page/link/image)
- Notes field for URL saves
- Signed and published on AMO

Other:
- Reader bookmark button routes to Brain (was Karakeep)
- Fitness food library with "Add" button + add-to-meal popup
- Kindle send file size check (25MB SMTP2GO limit)
- Atelier UI as default (useAtelierShell=true)
- Mobile upload box in nav drawer

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

gateway/integrations/kindle.py

@@ -90,8 +90,15 @@ def handle_send_to_kindle(handler, book_id: str, body: bytes):
     title = meta.get("title", "Book") if meta else "Book"
     author = ", ".join(meta.get("authors", [])) if meta else ""
 
-    # Read file and encode as base64
+    # Read file and check size
     file_data = file_path.read_bytes()
+    size_mb = len(file_data) / (1024 * 1024)
+    if size_mb > 25:
+        handler._send_json({
+            "error": f"File too large for email ({size_mb:.1f} MB). SMTP2GO limit is 25 MB. Use the Kindle app or USB instead.",
+            "size_mb": round(size_mb, 1),
+        }, 413)
+        return
     file_b64 = base64.b64encode(file_data).decode("ascii")
     filename = file_path.name
 
@@ -133,7 +140,9 @@ def handle_send_to_kindle(handler, book_id: str, body: bytes):
                 "size": len(file_data),
             })
         else:
-            handler._send_json({"error": "Email send failed", "detail": result}, 500)
+            failures = result.get("data", {}).get("failures", [])
+            detail = failures[0] if failures else str(result)
+            handler._send_json({"error": f"Email send failed: {detail}"}, 500)
     except Exception as e:
         handler._send_json({"error": f"SMTP2GO error: {str(e)}"}, 500)
 
@@ -175,6 +184,13 @@ def handle_send_file_to_kindle(handler, body: bytes):
         return
 
     file_data = file_path.read_bytes()
+    size_mb = len(file_data) / (1024 * 1024)
+    if size_mb > 25:
+        handler._send_json({
+            "error": f"File too large for email ({size_mb:.1f} MB). SMTP2GO limit is 25 MB. Use the Kindle app or USB instead.",
+            "size_mb": round(size_mb, 1),
+        }, 413)
+        return
     file_b64 = base64.b64encode(file_data).decode("ascii")
 
     ext = file_path.suffix.lower()