Restore features lost during main merge and fix workspace setup flow

Restores all features dropped when merging main into dev:
- Keyboard shortcuts (send, dictation-confirm) with full e2e chain
- Feature toggles (plan/fast mode) in agent status bar
- Sidebar kebab menu (Remove Project) on project rows
- Combined model selector (sticky header, sizing, favorites sort, search)
- Question form Enter key submit with guard
- Input focus restoration (composer + AgentStatusBar onDropdownClose)
- Draft-agent feature toggles and focus restoration
- Provider diagnostics UI (settings section, diagnostic sheet, status badge)
- Provider diagnostics server (snapshot manager, diagnostic utils, RPC)

Fixes dev-branch regressions:
- New workspace button now opens composer in setup dialog via beginWorkspaceSetup
- Setup tab auto-opens when workspace setup is running

packages/app/src/keyboard/keyboard-shortcuts.ts

@@ -860,6 +860,14 @@ const SHORTCUT_BINDINGS: readonly ShortcutBinding[] = [
     },
   },
 
+  {
+    id: "message-input-dictation-confirm-enter",
+    action: "message-input.action",
+    combo: "Enter",
+    when: { commandCenter: false, terminal: false },
+    payload: { type: "message-input", kind: "dictation-confirm" },
+  },
+
   {
     id: "message-input-voice-mute-toggle",
     action: "message-input.action",