feat(frontend): add SSE auto-reconnect with toast notifications

- Automatic reconnection with exponential backoff (1s to 30s max)
- Toast when connection is lost: 'Sunucu bağlantısı kesildi'
- Toast when reconnected: 'Sunucu bağlantısı yeniden kuruldu'
- Backend rTorrent notifications still work via SSE

frontend/Cargo.toml

@@ -16,6 +16,7 @@ log = "0.4"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 gloo-net = "0.5"
+gloo-timers = { version = "0.3", features = ["futures"] }
 wasm-bindgen = "0.2"
 uuid = { version = "1", features = ["v4", "js"] }
 futures = "0.3"