fix(tui): accept Alt+G as Ctrl+G fallback in VSCode/Cursor terminals

VSCode and Cursor bind Ctrl+G to "Find Next" at the editor level, so
the keystroke never reaches the embedded terminal — Ctrl+G to open
\$EDITOR was effectively dead inside those IDEs.

Alt+G is unbound in both editors and reaches the TUI cleanly as
`\x1bg` → `key.meta && ch === 'g'` after parse-keypress. Accept it
alongside the existing isAction(key, ch, 'g') check, and document the
fallback in README + the hotkeys panel.

ui-tui/src/content/hotkeys.ts

@@ -18,7 +18,7 @@ const copyHotkeys: [string, string][] = isMac
 export const HOTKEYS: [string, string][] = [
   ...copyHotkeys,
   [action + '+D', 'exit'],
-  [action + '+G', 'open $EDITOR for prompt'],
+  [action + '+G / Alt+G', 'open $EDITOR for prompt (Alt+G in VSCode/Cursor)'],
   [action + '+L', 'new session (clear)'],
   [paste + '+V / /paste', 'paste text; /paste attaches clipboard image'],
   ['Tab', 'apply completion'],