feat(tauri): add Windows taskbar overlay badge for git sync status

This change introduces a Windows-only taskbar badge that displays the
ahead+behind count as a rendered overlay icon. The UI now updates
the badge whenever the repository sync status changes, and the git
diff commands are adjusted to avoid external diff/text conversion noise.

- Add badge rendering and Tauri command for setting overlay icon
- Wire badge updates into the Svelte app based on git status
- Update git diff invocations to disable ext-diff/textconv

.claude/settings.local.json

@@ -73,7 +73,10 @@
       "Bash(rustup target *)",
       "Bash(echo \"exit code: $?\")",
       "Read(//home/cbr/.cargo/registry/src/**)",
-      "Bash(find / -maxdepth 6 -iname \"mistralrs-*\" -type d)"
+      "Bash(find / -maxdepth 6 -iname \"mistralrs-*\" -type d)",
+      "Bash(grep -A2 '^name = \"tauri\"$' \"/mnt/c/Users/cbr/Desktop/Neuer Ordner \\(6\\)/src-tauri/Cargo.lock\")",
+      "Bash(rustfmt --edition 2024 --check src/badge.rs src/main.rs)",
+      "Bash(rustfmt --edition 2024 --check src/git.rs)"
     ]
   }
 }