feat: store node logo/favicon in postgres instead of S3

- Add logoData and faviconData columns to nodes table
- Create /api/admin/node/upload endpoint for direct DB storage
- Create /api/node/logo and /api/node/favicon endpoints to serve images
- Update admin page to use new upload endpoint
- Remove dependency on admin's personal S3 storage for node assets

drizzle/0012_add_logo_favicon_data.sql

@@ -0,0 +1,3 @@
+-- Migration: Add logo_data and favicon_data columns for base64 storage
+ALTER TABLE "nodes" ADD COLUMN IF NOT EXISTS "logo_data" text;
+ALTER TABLE "nodes" ADD COLUMN IF NOT EXISTS "favicon_data" text;