refactor(maestro): route web keys through a command registry

One entry per command — stable id, plain-language label, key chord, run()
— replacing the ad-hoc keydown listeners in main.ts, catalog.ts, debug.ts
and attach.ts and the parallel SHORTCUTS constant in help.ts. The `?`
overlay now renders the registry, so a binding and its documentation
cannot disagree.

Keys are canonicalised the way the TUI's `InputKey::canonical` spells
them, and chords resolve like its `ChordState`: hold while the sequence
is a strict prefix, otherwise dispatch. That gives the web a leader,
`ctrl-a` by default like `[tui].leader`, held as a partial chord and
`preventDefault`ed so it stops being select-all — the escape hatch in
docs/COMMAND-BAR.md needs somewhere to land (#149). The leader stays out
of real form fields, where select-all is still what the operator wants.

Same keys, same effects: plain single-key bindings remain deaf inside
form fields and the terminal's hidden textarea, chorded ones do not.

Refs #148

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/src/debug.ts

@@ -2,6 +2,8 @@
 // survives reloads, flipped by a keybind (Ctrl+Shift+D), and force-enabled by
 // `?hud` in dev. A `maestro-hud-toggle` event lets the HUD re-render on change.
 
+import { CommandSet, defineCommands } from "./commands.js";
+
 const STORAGE_KEY = "maestro:hud";
 export const HUD_TOGGLE_EVENT = "maestro-hud-toggle";
 
@@ -31,12 +33,9 @@ export function toggleHud(): void {
   setHudEnabled(!isHudEnabled());
 }
 
+const hudKeys = new CommandSet(defineCommands({ "debug.toggleHud": () => toggleHud() }));
+
 /** Global keybind: Ctrl+Shift+D toggles the debug HUD. */
 export function installHudKeybind(): void {
-  window.addEventListener("keydown", (e) => {
-    if (e.ctrlKey && e.shiftKey && (e.key === "D" || e.key === "d")) {
-      e.preventDefault();
-      toggleHud();
-    }
-  });
+  window.addEventListener("keydown", (e) => hudKeys.handle(e));
 }