refactor(ext/vault): extract vault-drawer.ts + ensureDrawerClosedForRoute (Plan C Phase 4)

Moves the drawer (open/close/render + getDrawerCoreFields + selectItemForDrawer)
out of vault.ts into vault-drawer.ts, taking the VaultController ctx. Adds
ensureDrawerClosedForRoute(state, route) — called in renderPane before the view
switch — so drawer state cannot leak across navigation to non-list/detail
routes (P2 safety net). New drawer-state.test.ts covers it (TDD).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

extension/src/vault/__tests__/drawer-state.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from 'vitest';
+import { ensureDrawerClosedForRoute } from '../vault-drawer';
+
+describe('ensureDrawerClosedForRoute', () => {
+  it('closes the drawer when navigating to trash', () => {
+    const state = { drawerOpen: true };
+    ensureDrawerClosedForRoute(state, { view: 'trash' });
+    expect(state.drawerOpen).toBe(false);
+  });
+
+  it('leaves the drawer open when navigating to detail', () => {
+    const state = { drawerOpen: true };
+    ensureDrawerClosedForRoute(state, { view: 'detail' });
+    expect(state.drawerOpen).toBe(true);
+  });
+
+  it('leaves the drawer open in list view', () => {
+    const state = { drawerOpen: true };
+    ensureDrawerClosedForRoute(state, { view: 'list' });
+    expect(state.drawerOpen).toBe(true);
+  });
+
+  it('does nothing when the drawer is already closed', () => {
+    const state = { drawerOpen: false };
+    ensureDrawerClosedForRoute(state, { view: 'devices' });
+    expect(state.drawerOpen).toBe(false);
+  });
+});