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/vitest.config.ts

@@ -0,0 +1,12 @@
+import { defineConfig } from 'vitest/config'
+import react from '@vitejs/plugin-react'
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: ['./src/test/setup.ts'],
+    include: ['src/**/*.test.{ts,tsx}'],
+  },
+})