feat: add health checks, OG image generation, and R2 integration

- Implement health check system with caching and singleflight pattern
- Add OG image generation via Satori with R2 storage backend
- Configure Railway deployment with health check endpoint
- Add connection pooling and Unix socket support for Bun SSR
- Block external access to internal routes (/internal/*)

src/assets.rs

@@ -1,8 +1,8 @@
 use axum::{
-    http::{header, StatusCode, Uri},
+    http::{StatusCode, Uri, header},
     response::{IntoResponse, Response},
 };
-use include_dir::{include_dir, Dir};
+use include_dir::{Dir, include_dir};
 
 static CLIENT_ASSETS: Dir = include_dir!("$CARGO_MANIFEST_DIR/web/build/client");