fix(compact): size the window to the strip instead of a tuned constant

compactH was 158px, "tuned so the compact entry strip fits in a single row".
A constant tuned against a layout stops being true the moment the layout
changes, and this one outlived a strip that had since shrunk — leaving about
70px of empty window under the fields.

The frontend now measures what it rendered and asks for that height, watched by
a ResizeObserver so a strip that wraps at a narrow width is followed too. The
topbar is added as its declared h-8 rather than measured, since it is fixed.

Bounded in the backend: a measurement of zero — a layout not yet painted —
must not collapse the window, and the call is ignored unless compact is on so
nothing can shrink the normal window. Rounded to whole pixels so a sub-pixel
reflow cannot start a resize loop.

frontend/src/App.tsx

@@ -16,7 +16,7 @@ import {
   GetStartupStatus, CheckForUpdate, DownloadAndApplyUpdate, GetLiveStations, GetWhatsNew, GetChangelog,
   SMTPConfigured, SendLogToDeveloper,
   WorkedBefore,
-  SetCompactMode,
+  SetCompactMode, SetCompactHeight,
   GetCATState, SetCATFrequency, SetCATMode, SwitchCATRig, FlexApplyBandAntenna, FlexApplyBandPower,
   GetSecretStatus, UnlockSecrets,
   RefreshCtyDat, DownloadAllReferenceLists,
@@ -529,6 +529,28 @@ export default function App() {
     setCompact(next);
     SetCompactMode(next);
   }
+  // Fit the compact window to what was actually rendered.
+  //
+  // The height was a constant "tuned so the compact entry strip fits in a single
+  // row". A constant tuned against a layout stops being true the moment the
+  // layout changes, and this one outlived a strip that had since lost a row —
+  // leaving a band of empty window under the fields. Measure instead.
+  const compactRootRef = useRef<HTMLDivElement | null>(null);
+  useEffect(() => {
+    if (!compact) return;
+    const fit = () => {
+      const el = compactRootRef.current;
+      if (!el) return;
+      // Rounded, so a sub-pixel reflow cannot start a resize loop.
+      // + the compact topbar, which is a fixed h-8 (32px), + a couple of pixels
+      // for the border so the strip is never clipped by one row of anti-aliasing.
+      SetCompactHeight(Math.round(el.getBoundingClientRect().height) + 32 + 2);
+    };
+    const id = window.setTimeout(fit, 60); // let the strip paint first
+    const ro = new ResizeObserver(fit);
+    if (compactRootRef.current) ro.observe(compactRootRef.current);
+    return () => { window.clearTimeout(id); ro.disconnect(); };
+  }, [compact]);
 
   // CAT — receives live rig state via Wails events.
   const [catState, setCatState] = useState<CATState>({ enabled: false, connected: false } as any);
@@ -5892,7 +5914,7 @@ export default function App() {
           Enter from any <input> inside the strip logs the QSO. Radix Selects
           render as <button> elements and are ignored by this handler — they
           keep their own keyboard behaviour. */}
-      <div className={cn(!compact && 'flex gap-2.5 items-stretch px-2.5 pt-2.5 shrink-0')}>
+      <div ref={compactRootRef} className={cn(!compact && 'flex gap-2.5 items-stretch px-2.5 pt-2.5 shrink-0')}>
       <section
         className={cn('bg-card shadow-sm border-border',
           compact