v1.10.3: booterm mobile/UX fixes + global keyboard shortcuts

Five issues + keyboard shortcuts across booterm and the workspace shell.

Auto-switch on create (mobile): addSplitPane now returns the new pane id;
Session.tsx wraps it with addPaneAndSwitch which pushes ?pane=<newId> on
mobile so the URL-sync effect doesn't fight the just-set activePaneIdx.
NewPaneMenu uses the wrapper; desktop Split dropdown is unaffected.

Tab-away reconnect: TerminalPane has a connect()/manualReconnect() state
machine. ws.onclose backs off 500ms/1s/2s × 3 attempts, then surfaces a
[Disconnected] banner with a Reconnect button. visibilitychange listener
calls manualReconnect when the tab returns and the WS isn't OPEN. tmux
session persists server-side so scrollback is intact on resume.

Copy/paste: attachCustomKeyEventHandler binds Cmd/Ctrl-C (copy if
selection, else send ^C), Cmd/Ctrl-Shift-C (always swallow — copy if any,
no-op otherwise — never sends ^C), Cmd/Ctrl-V and Cmd/Ctrl-Shift-V
(navigator.clipboard.readText → ws.send). No custom right-click menu —
browser's native menu is preserved.

Scroll: removed `set -g mouse on` from tmux.conf so xterm.js sees wheel
and touch events natively. scrollback: 10_000, fastScrollModifier: 'shift',
altClickMovesCursor: false. Container has touch-action: pan-y for mobile.

Right-edge gap: inline <style> overrides xterm's defaults to width:100%
height:100% and hides the scrollbar chrome. Host container is
flex-1 min-w-0 self-stretch w-full. Three refit triggers: ResizeObserver
(rAF-wrapped), document.fonts.ready, and useEffect on the new active prop.
Background color matched between outer div, inner div, and xterm theme.

Keyboard shortcuts in Session.tsx (window-level keydown):
  Cmd/Ctrl+`              focus active terminal, else jump to last
  Cmd/Ctrl+Shift+T        new terminal pane
  Cmd/Ctrl+Shift+C        new chat pane (defers to xterm copy if focused)
  Cmd/Ctrl+W              close active pane
  Cmd/Ctrl+Tab/Shift+Tab  cycle next / prev pane
  Cmd/Ctrl+1..9           jump to pane N
terminalsRegistry gains a focus() callback per registration so Cmd+`
can call term.focus() on the active terminal.

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

apps/web/src/components/Workspace.tsx

@@ -271,6 +271,7 @@ export function Workspace({
                   sessionId={sessionId}
                   paneId={pane.id}
                   label={terminalLabels.get(pane.id) ?? 'Terminal'}
+                  active={idx === activePaneIdx}
                 />
               ) : pane.kind === 'chat' && pane.chatId ? (
                 <ChatPane