fix: v0.10.3 no tmux right-click menus; close split panes

Right-clicking a pane opened tmux's menu, whose Split entries left a stray
pane next to Claude (and whose Kill entries could end it). Unbind the
right-click menus; add --unsplit and a palette entry that closes extra
panes and keeps Claude's. Closes #52

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WHRLCCdXYm41Qx5kNhehaP

web/src/main.js

@@ -750,6 +750,16 @@ async function compact(session) {
   return undefined;
 }
 
+// A stray split (devdesk#52): close every extra pane, keeping Claude's.
+async function unsplit(session) {
+  try {
+    const result = await sessionAction('unsplit', session);
+    toast.success(result?.closed ? `Closed ${result.closed} pane${result.closed === 1 ? '' : 's'}` : 'No split panes');
+  } catch (error) {
+    toast.error(error.message);
+  }
+}
+
 async function copyLink() {
   const url = new URL(window.location.href);
   url.search = state.session ? `?arg=${encodeURIComponent(state.session)}` : '';
@@ -801,6 +811,7 @@ function buildCommands() {
     add({ id: 'win-shell', group: 'Terminal', icon: '1', label: 'Shell window', kbd: '^b 1', run: () => sendKeys('\x021') });
     add({ id: 'scroll', group: 'Terminal', icon: '⇞', label: 'Scroll back (tmux copy mode, q to leave)', kbd: '^b [', keywords: 'history scrollback', run: () => sendKeys('\x02[') });
     add({ id: 'detach', group: 'Terminal', icon: '⏏', label: 'Detach (the session keeps running)', kbd: '^b d', run: () => sendKeys('\x02d') });
+    add({ id: 'unsplit', group: 'Terminal', icon: '▣', label: 'Close split panes (keeps Claude)', keywords: 'pane split remove side by side layout', run: () => unsplit(state.session) });
   }
 
   if (state.session) {