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/*)

Cargo.toml

@@ -4,8 +4,11 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
+aws-config = "1.8.12"
+aws-sdk-s3 = "1.119.0"
 axum = "0.8.8"
 clap = { version = "4.5.54", features = ["derive", "env"] }
+futures = "0.3.31"
 include_dir = "0.7.4"
 mime_guess = "2.0.5"
 nu-ansi-term = "0.50.3"