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

Cargo.lock

@@ -695,6 +695,7 @@ dependencies = [
  "console_log",
  "futures",
  "gloo-net 0.5.0",
+ "gloo-timers",
  "js-sys",
  "leptos",
  "leptos_router",
@@ -874,6 +875,18 @@ dependencies = [
  "web-sys",
 ]
 
+[[package]]
+name = "gloo-timers"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbb143cf96099802033e0d4f4963b19fd2e0b728bcf076cd9cf7f6634f092994"
+dependencies = [
+ "futures-channel",
+ "futures-core",
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "gloo-utils"
 version = "0.2.0"