feat(shell): add Ctrl+/- zoom and display all shortcuts in footer

- Ctrl+/Ctrl-/Ctrl+0 to zoom in/out/reset terminal font size
- Zoom badge indicator in tab bar
- All shell shortcuts now shown in statusbar footer
- Added i18n labels for search, zoom, switch tab, next tab

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

web/src/i18n/en.js

@@ -18,6 +18,10 @@ const en = {
     newLine: 'New line',
     copy: 'Copy',
     paste: 'Paste',
+    search: 'Search',
+    zoom: 'Zoom +/−',
+    switchTab: 'Switch tab',
+    nextTab: 'Next tab',
     runCommand: 'Run command',
     commandHistory: 'Command history',
   },