feat(maestro): mobile special-key bar for web attach (NAP-342)

On touch devices the soft keyboard omits the keys terminals depend on
(Esc, Tab, Ctrl, arrows, Home/End, PgUp/PgDn). Add a Termux-style
scrollable key bar to the attach view that injects the right xterm
sequences into the existing PTY input path.

- Ctrl is a one-shot sticky modifier: arm it and the next character —
  tapped here or typed on the soft keyboard — is sent as its control
  code, so Ctrl+C and friends work on mobile.
- Taps preventDefault on pointerdown so the terminal keeps focus and the
  keyboard stays open.
- Bar is revealed only on coarse-pointer devices; a physical keyboard
  already has these keys.
- Shell height now tracks the visual viewport (installViewportSizing) so
  the bar lands above the soft keyboard instead of behind it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/main.ts

@@ -4,9 +4,11 @@ import { CatalogStore } from "./events.js";
 import { openSpawnModal } from "./spawn.js";
 import { initTheme } from "./theme.js";
 import { sessionName } from "./types.js";
+import { installViewportSizing } from "./viewport.js";
 import "./styles.css";
 
 initTheme();
+installViewportSizing();
 
 const rootEl = document.getElementById("app");
 if (!rootEl) {