address review (codex): debounce inline Python path input, gate arch warning to darwin/arm64

* LocalSetupPanel: the inline path input fired onPythonPathChange on
  every keystroke. In the VideoGen consumer that meant a settings PATCH
  + a ~1-2s status re-probe per character. Decouple via local draft
  state; commit on 800ms debounce or onBlur. Programmatic updates
  (Detect, Switch-to-arm64, Create-venv) still call onPythonPathChange
  directly so they take effect immediately.
* /api/image-gen/setup/check: generic interpreterArch !== HOST_ARCH
  would false-positive on Windows (Python reports `AMD64` vs Node's
  `x86_64`) and on hypothetical arm64 Linux where mlx isn't even in
  REQUIRED_PACKAGES. Gate the warning to darwin/arm64 with an x86_64
  interpreter — the only configuration where mlx actually breaks.

The third codex finding (hfDownload.js falls back to broken FLUX.2 venv)
is in a file not yet on origin and not part of this PR's surface; left
for whichever branch ships hfDownload.

Author: atomantic

client/src/components/settings/LocalSetupPanel.jsx

@@ -12,6 +12,25 @@ export default function LocalSetupPanel({ pythonPath, onPythonPathChange, onPack
   const [creatingVenv, setCreatingVenv] = useState(false);
   const logRef = useRef(null);
   const installEsRef = useRef(null);
+  // Decouple the input from the parent's persisted path. The VideoGen
+  // consumer saves on every onPythonPathChange, so wiring the input to the
+  // prop directly fires a settings PATCH + ~1-2s status re-probe per
+  // keystroke. Typed edits commit on debounce/blur; programmatic updates
+  // (Detect, Switch-to-arm64, Create-venv) still call onPythonPathChange
+  // directly so they take effect immediately.
+  const [draftPath, setDraftPath] = useState(pythonPath || '');
+  const commitTimerRef = useRef(null);
+  useEffect(() => { setDraftPath(pythonPath || ''); }, [pythonPath]);
+  useEffect(() => () => clearTimeout(commitTimerRef.current), []);
+  const commitDraft = (value) => {
+    clearTimeout(commitTimerRef.current);
+    if (value !== (pythonPath || '')) onPythonPathChange(value);
+  };
+  const handleDraftChange = (value) => {
+    setDraftPath(value);
+    clearTimeout(commitTimerRef.current);
+    commitTimerRef.current = setTimeout(() => commitDraft(value), 800);
+  };
 
   // Closing the install EventSource on unmount stops setInstalling /
   // setInstallLog calls firing on a torn-down component if the user
@@ -143,8 +162,9 @@ export default function LocalSetupPanel({ pythonPath, onPythonPathChange, onPack
       <div className="flex items-center gap-2">
         <input
           type="text"
-          value={pythonPath || ''}
-          onChange={(e) => onPythonPathChange(e.target.value)}
+          value={draftPath}
+          onChange={(e) => handleDraftChange(e.target.value)}
+          onBlur={() => commitDraft(draftPath)}
           className="flex-1 bg-port-bg border border-port-border rounded-lg px-3 py-2 text-sm text-white focus:outline-none focus:border-port-accent"
           placeholder="/usr/local/bin/python3"
         />

server/routes/imageGen.js

@@ -685,7 +685,13 @@ router.get('/setup/check', asyncHandler(async (req, res) => {
     return res.status(400).json({ error: 'pythonPath must be a python interpreter (basename python/python3/python3.NN)' });
   }
   const health = await probePythonHealth(pythonPath);
-  const archMismatch = !!(health.interpreterArch && health.interpreterArch !== HOST_ARCH);
+  // The arch warning is specifically about mlx wheels (arm64-only) on Apple
+  // Silicon. A generic interpreterArch !== HOST_ARCH compare would false-
+  // positive on Windows (Python reports `AMD64`, Node reports `x86_64`) and
+  // on hypothetical arm64 Linux — where mlx isn't even in REQUIRED_PACKAGES.
+  const archMismatch = process.platform === 'darwin'
+    && HOST_ARCH === 'arm64'
+    && health.interpreterArch === 'x86_64';
   const suggestedArm64Python = archMismatch ? await detectArm64Python() : null;
   res.json({
     pythonPath,