Add embedded Nostr relay with catch-up sync on startup

Embedded relay (strfry-lite in Rust) stores events locally in SQLite.
On startup, syncs user notes, follow feed (24h), mentions (7d), and
profile/contacts from remote relays into the local relay. Uses since
timestamp for incremental syncs. Toggle in Settings with event count
and DB size display. Add webkit2gtk GPU acceleration workaround and
connectToRelays safety timeout for NDK hang.

src-tauri/Cargo.toml

@@ -30,4 +30,13 @@ tauri-plugin-http = "2.5.7"
 tauri-plugin-dialog = "2.6.0"
 tauri-plugin-fs = "2.4.5"
 tauri-plugin-notification = "2.3.3"
+tokio = { version = "1", features = ["rt-multi-thread", "net", "sync", "macros", "time"] }
+tokio-tungstenite = "0.24"
+secp256k1 = { version = "0.30", features = ["global-context"] }
+sha2 = "0.10"
+hex = "0.4"
+futures-util = "0.3"
+
+[target.'cfg(target_os = "linux")'.dependencies]
+webkit2gtk = "2.0"