fix(vst-gui): borderless fx-gui window + anchored re-show (mouse stable)

- RenderFxJob: offscreen fx-gui window now WS_POPUP (borderless) so
  GetWindowRect == client rect; anchored placement over the embed panel is
  exact. WS_OVERLAPPEDWINDOW put the client ~31px lower/right -> cursor
  jumped on hover and clicks hit the webview (relay rejected).
- AdjustWindowRect sizes to the window's own style (no caption for POPUP).
- FxGuiServer: mousemove only SetCursorPos while dragging (buttons!=0);
  hover no longer teleports the cursor.
- FxGuiServer /show: skip SetWindowPos/resize when rect unchanged (frontend
  now re-POSTs /show every ~500ms to re-anchor on scroll/resize).
- app.jsx VstGuiEmbed: drop shownRef one-shot; re-POST /show each refresh.
- Rebuilt bridge (6 locations) + Tauri release (embedded sidecar) + v=202608190002.

app/static/js/app.jsx

@@ -11909,7 +11909,6 @@ const ExportModal = ({ open, onClose, exportSettings, setExportSettings, isExpor
     const boxRef = React.useRef(null);
     const deadRef = React.useRef(false);
     const screenRectRef = React.useRef(null);
-    const shownRef = React.useRef(false);
     const [dead, setDead] = React.useState(false);
     const post = (payload) => { try { fetch(url + '/input', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify(payload) }).catch(() => {}); } catch (e) {} };
     React.useEffect(() => {
@@ -11936,10 +11935,10 @@ const ExportModal = ({ open, onClose, exportSettings, setExportSettings, isExpor
       let alive = true;
       const maybeShow = () => {
         const r = screenRectRef.current;
-        if (!shownRef.current && r && r.w >= 4 && r.h >= 4) {
-          shownRef.current = true;
-          // Show the native window anchored over the panel (bridge stays
-          // alive; hidden again by /hide on unmount).
+        if (r && r.w >= 4 && r.h >= 4) {
+          // Re-POST /show on every refresh (~500ms) so the native window
+          // re-anchors over the panel on scroll/drag/resize. Idempotent: the
+          // bridge skips SetWindowPos/resize when nothing moved.
           try { fetch(url + '/show', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ rect: r }) }).catch(() => {}); } catch (e) {}
         }
       };