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

CHANGELOG.md

@@ -6,6 +6,14 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ---
 
+## [1.2.1] - 2026-05-17
+
+### Added
+
+- **Version footer** — the dashboard footer now displays the running app version (e.g. `sofarr v1.2.1`), fetched from the `/health` endpoint on page load.
+
+---
+
 ## [1.2.0] - 2025-05-17
 
 ### Security