docs: rewrite PLAN.md and update CODEBASE.md, README.md

- Full rewrite of PLAN.md to reflect current architecture (27 REST + 3 WS endpoints,
  embedded frontend, automation, scheduler, health check, GoReleaser CI)
- Added health.go, mods.go, scheduler.go, robfig/cron dep to CODEBASE.md
- Added Gitea Actions CI/CD section to CODEBASE.md
- Added conventional commits to code style section
- Added missing API routes and embed/ to README.md

frontend/src/components/Layout.test.tsx

@@ -0,0 +1,49 @@
+import { describe, it, expect } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { MemoryRouter } from 'react-router-dom'
+import Layout from './Layout'
+
+describe('Layout', () => {
+  it('renders sidebar navigation', () => {
+    render(
+      <MemoryRouter>
+        <Layout>
+          <div>Content</div>
+        </Layout>
+      </MemoryRouter>
+    )
+
+    expect(screen.getByText('Dashboard')).toBeInTheDocument()
+    expect(screen.getByText('Settings')).toBeInTheDocument()
+    expect(screen.getByText('Configs')).toBeInTheDocument()
+    expect(screen.getByText('Modlists')).toBeInTheDocument()
+    expect(screen.getByText('Mods')).toBeInTheDocument()
+    expect(screen.getByText('Logs')).toBeInTheDocument()
+    expect(screen.getByText('Status')).toBeInTheDocument()
+  })
+
+  it('renders children', () => {
+    render(
+      <MemoryRouter>
+        <Layout>
+          <div>Test Content</div>
+        </Layout>
+      </MemoryRouter>
+    )
+
+    expect(screen.getByText('Test Content')).toBeInTheDocument()
+  })
+
+  it('highlights active route', () => {
+    render(
+      <MemoryRouter initialEntries={['/settings']}>
+        <Layout>
+          <div>Content</div>
+        </Layout>
+      </MemoryRouter>
+    )
+
+    const settingsLink = screen.getByText('Settings')
+    expect(settingsLink).toHaveClass('text-white')
+  })
+})