feat: Add About section with version info and update check (#50)

* feat: add About section with version info and update check

- Add About menu item in user dropdown
- Show frontend and backend versions separately
- Add 'Check for Updates' feature using GitHub API
- Compare versions using semver logic
- Cache update check results in sessionStorage (1 hour TTL)
- Link to GitHub repository
- Add i18n translations for EN and DE
- Extend health endpoint to return backend version

* fix: correct i18n interpolation in About modal

- Fix copyright year using dynamic interpolation
- Fix update available message (remove duplicate version placeholder)
- Add download link for available updates
- Change license to GPL-3.0

* fix: correct license to MIT

* chore: sync package.json versions to v1.3.1

backend/src/routes/health.ts

@@ -1,8 +1,18 @@
 import { FastifyInstance } from "fastify";
+import { readFileSync } from "fs";
+import { resolve, dirname } from "path";
+import { fileURLToPath } from "url";
+
+// Read version from package.json at startup
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const packageJsonPath = resolve(__dirname, "../../package.json");
+const packageJson = JSON.parse(readFileSync(packageJsonPath, "utf-8"));
+const backendVersion = packageJson.version || "unknown";
 
 export async function healthRoutes(app: FastifyInstance) {
   app.get("/health", async () => ({
     status: "ok",
+    version: backendVersion,
     smtpConfigured: Boolean(process.env.SMTP_HOST),
     shoutrrrConfigured: Boolean(process.env.SHOUTRRR_URL),
   }));