fix(dashboard): UI polish — modals, layout, consistency, test fixes

Dashboard UX polish pass — consolidates create forms into modals
triggered from the page header, fixes layout inconsistencies, adds
scroll-to navigation for the Keys page, and aligns the TokenBar with
the design system.

Changes:
- App.tsx: add padding to sidebar header
- resolve-page-title.ts: add missing routes, better fallback title
- en.ts: fix nav labels (Profiles was 'profiles : multi agents')
- ModelsPage: two-col layout, auxiliary tasks modal, TokenBar redesign
- ProfilesPage: create button in header, form in modal, Checkbox component
- CronPage: create button in header, form in modal
- EnvPage: scroll-to sub-nav in header, fix text overflow

Modal and dialog standardization:
- Replace all native confirm()/window.confirm() with ConfirmDialog
  (OAuthProvidersCard, PluginsPage, ModelsPage, ConfigPage)
- Add useModalBehavior hook (Escape-to-close, scroll lock, focus restore)
- Apply hook to ProfilesPage, CronPage, AuxiliaryTasksModal

Component fixes (from PR review):
- Checkbox: fix controlled/uncontrolled mismatch, add focus-visible ring
- TokenBar: add rounded-full to legend dots, remove dead code

CI/test fixes:
- Fix TS unused imports (noUnusedLocals), type-narrow PickerTarget union
- Add windows-footgun suppression on platform-guarded os.killpg
- Fix 19 stale unit tests + 9 e2e tests broken by recent main changes
- Restore minimal example-dashboard plugin for plugin auth test

plugins/example-dashboard/dashboard/plugin_api.py

@@ -0,0 +1,17 @@
+"""Example dashboard plugin — backend API routes.
+
+Mounted at /api/plugins/example/ by the dashboard plugin system.
+
+This minimal plugin exists so the test suite has a stable, side-effect-free
+GET endpoint to verify that plugin API routes work with auth.
+"""
+
+from fastapi import APIRouter
+
+router = APIRouter()
+
+
+@router.get("/hello")
+async def hello():
+    """Simple greeting endpoint to demonstrate plugin API routes."""
+    return {"message": "Hello from the example plugin!", "plugin": "example", "version": "1.0.0"}