feat(git): add upstream tracking and local-only branch UI

This release adds upstream tracking for branches and a local-only
indicator in the UI.
The Git integration now exposes upstreams and supports publish flows.
This enables publishing and remote-tracking configuration.

- Introduces upstream tracking and local-only branch UI markers
- Updates toolbar to reflect publish-local state and status indicators
- Bumps version to 2026.8.3 and updates changelog

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "Gitty",
-  "version": "2026.8.2",
+  "version": "2026.8.3",
   "identifier": "com.gitty",
   "build": {
     "beforeDevCommand": "npm run dev",