[GUI] Health check polling doesn't detect daemon crash

[Vantalens]

File: packages/gui/src-tauri/src/lib.rs:72

Severity: Medium

Description:
Daemon crashes immediately after spawn; loop sleeps 10 seconds (40 × 250ms) checking port that will never open instead of detecting early exit via child.try_wait().

Code:

for _ in 0..40 {
    std::thread::sleep(Duration::from_millis(250));
    if is_daemon_healthy(config.port) {
        return Ok(...);
    }
}

Failure Scenario:

• Spawn daemon with invalid config (missing provider, bad port, etc.)
• Daemon crashes within 100ms
• Health check loops for full 10 seconds checking dead port
• User waits unnecessarily; slow startup experience

Suggested Fix:
Check child.try_wait() each iteration; if process exited, fail immediately with stderr output.