feat: add Community/Pro licensing, fleet view, and UI reorganization (#145)

* feat: add license gating system with Lemon Squeezy integration

Add Community/Pro tier infrastructure:
- LicenseService singleton with Lemon Squeezy license API integration
- /api/license endpoints (GET info, POST activate/deactivate/validate)
- 14-day Pro trial activated automatically on first boot
- 72-hour periodic validation with 30-day offline grace period
- LicenseContext provider for frontend tier awareness
- License settings tab with activation UI and status display
- ProBadge and ProGate reusable components for feature gating
- requirePro per-route guard for backend Pro-only endpoints
- Proxy bypass for /api/license routes (local-only, never proxied)

* feat: add user profile dropdown and reorganize top navigation

- Create UserProfileDropdown component with settings, billing, theme
  toggle (System/Light/Dark), documentation links, and logout button
- Remove logout button from sidebar header
- Remove standalone settings button from top bar
- Move theme toggle from Settings modal to profile dropdown
- Inject app version via Vite define from root package.json
- Add globals.d.ts for __APP_VERSION__ type declaration

* refactor(settings): remove appearance tab from settings modal

Theme toggle was moved to the User Profile Dropdown in the previous
commit. Remove the now-redundant Appearance section, its nav button,
and the unused theme/setTheme props from SettingsModal.

* feat: add fleet view dashboard and about settings section

Fleet Overview: aggregates all nodes into a card grid showing status,
container counts, CPU/RAM/disk usage bars. Pro tier unlocks stack
drill-down with auto-refresh (30s). Backend endpoints /api/fleet/overview
and /api/fleet/node/:nodeId/stacks query nodes in parallel.

About section in Settings: displays version, license tier, status,
instance ID, and links to docs/changelog/issues.

Sidebar perf fix: stack status fetches now run in parallel via
Promise.allSettled instead of sequential for-loop, significantly
reducing load time for nodes with many stacks.

Also removes version number from User Profile Dropdown (now in About).

* fix(ci): resolve Docker build and E2E test failures

- Copy root package.json into frontend build stage so vite.config.ts
  can read the app version during Docker multi-stage build.
- Update auth E2E test: logout button moved into User Profile Dropdown.
- Update nodes E2E test: Settings button moved into User Profile Dropdown.

frontend/vite.config.ts

@@ -2,10 +2,16 @@ import { defineConfig } from 'vite'
 import tailwindcss from '@tailwindcss/vite'
 import react from '@vitejs/plugin-react'
 import path from 'path'
+import { readFileSync } from 'fs'
+
+const rootPkg = JSON.parse(readFileSync(path.resolve(__dirname, '../package.json'), 'utf-8'));
 
 // https://vite.dev/config/
 export default defineConfig({
   plugins: [react(), tailwindcss()],
+  define: {
+    __APP_VERSION__: JSON.stringify(rootPkg.version),
+  },
   resolve: {
     alias: {
       "@": path.resolve(__dirname, "./src"),