feat: Semantische Versionierung mit Git-Tags und App-Footer.

VERSION-Datei (0.1.0.0), Release-Flow in update-prod.sh und Build-time-Einbindung der Versionsnummer im Footer mit Copyright-Link.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/vite.config.ts

@@ -1,9 +1,28 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 import { VitePWA } from 'vite-plugin-pwa'
+import { readFileSync } from 'node:fs'
+import { resolve, dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const __dirname = dirname(fileURLToPath(import.meta.url))
+
+function readAppVersion(): string {
+  if (process.env.VITE_APP_VERSION) {
+    return process.env.VITE_APP_VERSION.trim()
+  }
+  try {
+    return readFileSync(resolve(__dirname, '../VERSION'), 'utf8').trim()
+  } catch {
+    return '0.1.0.0-dev'
+  }
+}
 
 // https://vite.dev/config/
 export default defineConfig({
+  define: {
+    __APP_VERSION__: JSON.stringify(readAppVersion())
+  },
   server: {
     port: 5173,
     proxy: {