[DOCS] Migrate documentation from VuePress 1.x to VitePress (#2299)

- Replace VuePress 1.9.10 with VitePress 1.6.4
- Convert config from CommonJS to ESM TypeScript (config.mts)
- Convert shared Theengs nav config to ESM (commonConfig.mts)
- Rewrite BoardEnvironmentTable in Vue 3 Composition API
- Rewrite FlashEnvironmentSelector in Vue 3 Composition API
- Enable built-in local search and dark mode
- Add medium-zoom for image zoom
- Use VitePress CSS variables for dark mode compatibility
- Update CI script paths from .vuepress to .vitepress
- Update .gitignore for VitePress build artifacts
- Rename README.md files to index.md (VitePress convention)
- Fix markdown compatibility (angle-bracket escaping, image paths)
- Drop PWA plugin (not needed)

Co-authored-by: Florian <1technophile@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/.vitepress/commonConfig.mts

@@ -0,0 +1,41 @@
+// docs/.vitepress/commonConfig.mts
+// Adapter that loads the shared Theengs commonConfig.js (CommonJS) downloaded
+// by CI from https://www.theengs.io/commonConfig.js, and re-exports the nav
+// and head arrays in a format VitePress can consume.
+//
+// This keeps theengs.io as the single source of truth for nav/head until all
+// Theengs docs sites are migrated to VitePress.
+
+import { createRequire } from 'module'
+import { existsSync } from 'fs'
+import { resolve, dirname } from 'path'
+import { fileURLToPath } from 'url'
+
+const __dirname = dirname(fileURLToPath(import.meta.url))
+const require = createRequire(import.meta.url)
+
+const commonConfigPath = resolve(__dirname, 'public/commonConfig.js')
+
+let sharedConfig: any = null
+
+if (existsSync(commonConfigPath)) {
+  sharedConfig = require(commonConfigPath)
+} else {
+  console.warn(
+    'commonConfig.js not found in .vitepress/public/. ' +
+    'Using fallback nav/head. Run CI or download from https://www.theengs.io/commonConfig.js'
+  )
+}
+
+// Re-export nav from shared config, or use a minimal fallback
+export const commonNav = sharedConfig?.themeConfig?.nav ?? [
+  { text: 'Home', link: 'https://www.theengs.io' },
+  { text: 'Community', link: 'https://community.openmqttgateway.com' },
+  { text: 'Shop', link: 'https://shop.theengs.io/' }
+]
+
+// Re-export head from shared config, or use a minimal fallback
+export const commonHead = sharedConfig?.head ?? [
+  ['meta', { name: 'viewport', content: 'width=device-width, initial-scale=1' }],
+  ['meta', { name: 'theme-color', content: '#3eaf7c' }]
+]