fix(desktop): exit cleanly on fatal setup errors instead of SIGABRT

Setup errors inside tao's `did_finish_launching` FFI callback propagate
as `Err` to Tauri's `panic!("Failed to setup app: {e}")`. Because Rust
cannot unwind across an `extern "C"` boundary, this escalates to
`panic_cannot_unwind` → SIGABRT. macOS treats SIGABRT as a crash and
auto-relaunches the app, producing a 6-crash pile-up before giving up.
This is a known upstream issue (tao#1171, still open).

Convert the two fatal `?` operators in the setup closure (identity
resolution and keys mutex access) to explicit `eprintln! +
process::exit(1)`. A clean exit produces no crash report and macOS does
not auto-relaunch, breaking the crash-loop.

desktop/src-tauri/src/lib.rs

@@ -423,8 +423,10 @@ pub fn run() {
             // that will be lost on restart, as that silently breaks channel
             // memberships, DMs, and relay identity.
             let state = app_handle.state::<AppState>();
-            resolve_persisted_identity(&app_handle, &state)
-                .map_err(|e| -> Box<dyn std::error::Error> { e.into() })?;
+            if let Err(e) = resolve_persisted_identity(&app_handle, &state) {
+                eprintln!("buzz-desktop: fatal: identity resolution failed: {e}");
+                std::process::exit(1);
+            }
 
             // When the identity is in recovery mode (lost = keyring empty after
             // migration, or keyring-locked = keyring unreachable but marker
@@ -441,11 +443,13 @@ pub fn run() {
 
             // Snapshot owner keys after identity resolution; the best-effort
             // event reconcile itself runs off the synchronous setup path below.
-            let owner_keys = state
-                .keys
-                .lock()
-                .map(|k| k.clone())
-                .map_err(|e| -> Box<dyn std::error::Error> { e.to_string().into() })?;
+            let owner_keys = match state.keys.lock() {
+                Ok(k) => k.clone(),
+                Err(e) => {
+                    eprintln!("buzz-desktop: fatal: identity keys poisoned: {e}");
+                    std::process::exit(1);
+                }
+            };
 
             // Backfill the pinned persona snapshot for any pre-existing agent
             // that predates the record-authoritative-spawn cutover (persona_id