Lock titlebar + pane toolbar height to stop periodic xterm reflow

When the window or a pane was narrow, button text could wrap inside
flex items, growing the toolbar by ~16px. That shrank .pane-wrap →
ResizeObserver fired on every xterm → fit() reflowed text. Idle
detection toggling " · N idle" in the titlebar was enough to flap a
button across its wrap threshold every few seconds.

Lock both bars to fixed heights with white-space:nowrap, flex-shrink:0
on children, and overflow:hidden. Items that don't fit clip silently
instead of wrapping.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/App.css

@@ -16,6 +16,19 @@
   font-size: 12px;
   color: #aaa;
   user-select: none;
+  /* Lock to a single row even when the window is narrow: buttons whose
+     text would otherwise wrap (e.g. "📡 all off") would grow the
+     titlebar, shrink .pane-wrap, and reflow every xterm. nowrap stops
+     text-wrap inside buttons, flex-shrink:0 stops children from being
+     squeezed, height locks the row height, overflow:hidden clips items
+     that don't fit (widen the window to see them). */
+  white-space: nowrap;
+  height: 34px;
+  box-sizing: border-box;
+  overflow: hidden;
+}
+.titlebar > * {
+  flex-shrink: 0;
 }
 .titlebar .label {
   font-weight: 600;

src/lib/layout/LeafPane.css

@@ -58,7 +58,17 @@
   font-size: 11px;
   color: #aaa;
   user-select: none;
-  min-height: 24px;
+  height: 24px;
+  box-sizing: border-box;
+  /* Lock height: a narrow pane used to wrap toolbar items to 2+ rows,
+     which shrank the xterm beneath and reflowed the terminal. Clip
+     overflow instead of showing a scrollbar (which would itself eat
+     into the 24px and crush the buttons). */
+  white-space: nowrap;
+  overflow: hidden;
+}
+.pane-toolbar > * {
+  flex-shrink: 0;
 }
 .pane-label {
   font: inherit;