feat(v2): add agent tree, status bar, notifications, settings dialog (Phase 5)

Agent tree visualization (SVG) with horizontal layout and bezier edges.
Global status bar with pane counts, active agents pulse, token/cost totals.
Toast notification system with auto-dismiss and agent dispatcher integration.
Settings dialog with SQLite persistence for shell, cwd, and max panes.
Keyboard shortcuts: Ctrl+W close pane, Ctrl+, open settings.

v2/src/lib/adapters/settings-bridge.ts

@@ -0,0 +1,13 @@
+import { invoke } from '@tauri-apps/api/core';
+
+export async function getSetting(key: string): Promise<string | null> {
+  return invoke('settings_get', { key });
+}
+
+export async function setSetting(key: string, value: string): Promise<void> {
+  return invoke('settings_set', { key, value });
+}
+
+export async function listSettings(): Promise<[string, string][]> {
+  return invoke('settings_list');
+}