fix: _jack_is_operational() must check jack_lsp stdout, not exit code

jack_lsp on JACK 1.9.22 always exits 0 even when JACK is dead —
it prints error to stderr but returns success. Check for non-empty
stdout (port names) instead, which only appears when JACK is truly
operational.

src/system/audio.py

@@ -854,20 +854,19 @@ def _jack_is_running() -> bool:
 def _jack_is_operational() -> bool:
     """Check if JACK is actually accepting client connections.
 
-    Uses ``jack_lsp`` to verify the JACK server is operational beyond
+    Uses ``jack_lsp`` and checks stdout is non-empty (port names).
-    just having a running process. ``jack_lsp`` connects to the JACK
+    ``jack_lsp`` always exits 0 on JACK 1.9.22 even when dead —
-    server via shared memory and lists ports — it only succeeds when
+    only stdout content distinguishes 'JACK running' from
-    JACK has fully initialized the ALSA device and IPC is live.
+    'JACK inaccessible'.
-
-    On JACK 1.9.22 there is no ``/dev/shm/jack_default_0_0`` socket,
-    so ``jack_lsp`` is the most reliable readiness check.
     """
     try:
         result = subprocess.run(
             ["jack_lsp"],
             capture_output=True, timeout=3,
         )
-        return result.returncode == 0
+        # jack_lsp exits 0 even when dead on JACK 1.9.22 —
+        # only non-empty stdout means ports were actually listed
+        return bool(result.stdout.strip())
     except (FileNotFoundError, subprocess.TimeoutExpired):
         return False