feat: add version footer to dashboard UI (v1.2.1)

- /health endpoint now includes version field
- Footer displays 'sofarr vX.Y.Z' fetched on page load
- Subtle .app-version styling (smaller, dimmed)
- Bump version to 1.2.1, update CHANGELOG

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sofarr",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "A personal media download dashboard that shows your downloads 'so far' while you relax on the sofa waiting for your *arr services to finish",
   "main": "server/index.js",
   "scripts": {