feat(git-lfs): add Git LFS status and sidecar bundling

Adds Git LFS support to the backend API and related UI.
The app now exposes commands to inspect, install, track and pull.
A sidecar git-lfs binary is bundled and a prep script is added.
This prepares the correct binary for each target platform.

- Expose Git LFS status and management commands in API
- Bundle and prepare a sidecar git-lfs binary for targets
- Update packaging, docs, and README with LFS notes

docs/api-contract.md

@@ -73,6 +73,34 @@ interface GitRepositoryFile {
   tracked: boolean;
   status: FileStatusKind | null;
 }
+
+interface GitLfsStatus {
+  available: boolean;
+  bundled: boolean;
+  version: string | null;
+  filters_configured: boolean;
+  hook_installed: boolean;
+  repository_uses_lfs: boolean;
+  patterns: GitLfsPattern[];
+  files: GitLfsFile[];
+}
+
+interface GitLfsPattern {
+  pattern: string;
+  source: string;
+  lockable: boolean;
+  tracked: boolean;
+}
+
+interface GitLfsFile {
+  name: string;
+  size: number;
+  checkout: boolean;
+  downloaded: boolean;
+  oid_type: string;
+  oid: string;
+  version: string;
+}
 ```
 
 ## Commands
@@ -83,6 +111,14 @@ The command list below includes the repository-management and synchronization AP
 - `init_repository(path: string, initialBranch?: string): Promise<GitStatus>`
 - `clone_repository(...): Promise<RepositoryBundle>`
 - `get_status(path: string): Promise<GitStatus>`
+- `git_lfs_status(path: string): Promise<GitLfsStatus>`
+- `git_lfs_install(path: string): Promise<GitLfsStatus>`
+- `git_lfs_track(path: string, pattern: string, lockable?: boolean): Promise<GitLfsStatus>`
+- `git_lfs_untrack(path: string, pattern: string): Promise<GitLfsStatus>`
+- `git_lfs_pull(path: string, remote?: string, username?: string, password?: string): Promise<GitLfsStatus>`
+- `git_lfs_prune(path: string): Promise<GitLfsStatus>`
+- `pull(...)` automatically runs `git lfs pull` after a successful Git pull when
+  the repository contains LFS attributes or tracked LFS objects.
 - `list_branches(path: string): Promise<GitBranch[]>`
 - `list_remotes(path: string): Promise<GitRemote[]>`
 - `add_remote(path: string, name: string, url: string): Promise<GitRemote[]>`