feat(desktop): non-fatal sidecar spawn; verified real window renders under xvfb

If the sidecar can't start (missing binary, port already in use), log and keep
the window on the splash instead of aborting the whole app — better failure UX,
and it lets `cargo run` dev attach to an externally-run `openkb-api`.

Verified end-to-end: built the web UI, ran openkb-api on :8765, launched the
Tauri binary under xvfb (WebKitGTK). The shell polled the server, navigated off
the splash, and rendered the real Workbench UI — confirming the full
shell → poll → navigate → render flow works.

Claude-Session: https://claude.ai/code/session_01KZyUSGAzVL9yxpsWWPv6Y2

Author: claude

desktop/src-tauri/src/main.rs

@@ -68,8 +68,16 @@ fn main() {
     tauri::Builder::default()
         .manage(Sidecar(Mutex::new(None)))
         .setup(|app| {
-            let child = spawn_sidecar(app)?;
-            app.state::<Sidecar>().0.lock().unwrap().replace(child);
+            // Non-fatal: if the sidecar can't start (missing binary, port in
+            // use), keep the window up on the splash rather than crashing the
+            // app. In `cargo run` dev the bundled sidecar isn't present, so
+            // this lets the shell attach to an externally-run `openkb-api`.
+            match spawn_sidecar(app) {
+                Ok(child) => {
+                    app.state::<Sidecar>().0.lock().unwrap().replace(child);
+                }
+                Err(e) => eprintln!("openkb: could not spawn sidecar: {e}"),
+            }
 
             let url = format!("http://{HOST}:{PORT}/");
             let handle = app.handle().clone();