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

src/lib/RepoToolbar.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
   import {
+    Box,
     ChevronDown,
     Code2,
     CloudDownload,
@@ -41,6 +42,7 @@
   export let onFetchPrune: () => void = () => {};
   export let onForcePush: () => void = () => {};
   export let onSyncOptions: () => void = () => {};
+  export let onOpenLfs: () => void = () => {};
 
   let historyOpen = false;
   let syncOpen = false;
@@ -142,6 +144,7 @@
             <button type="button" role="menuitem" onclick={() => { syncOpen = false; onFetchPrune(); }}><CloudDownload size={15} /><span><strong>Fetch + Prune</strong><small>{isGerman ? "Veraltete Remote-Branches entfernen" : "Remove stale remote branches"}</small></span></button>
             <button type="button" role="menuitem" onclick={() => { syncOpen = false; onForcePush(); }}><Upload size={15} /><span><strong>Force with lease</strong><small>{isGerman ? "Sicheres Pushen nach Rebase" : "Safe push after rebase"}</small></span></button>
             <button type="button" role="menuitem" onclick={() => { syncOpen = false; onSyncOptions(); }}><Settings2 size={15} /><span><strong>{isGerman ? "Remotes & Strategien" : "Remotes & strategies"}</strong><small>{isGerman ? "Upstream, Pull und Remote verwalten" : "Manage upstream, pull and remotes"}</small></span></button>
+            <button type="button" role="menuitem" onclick={() => { syncOpen = false; onOpenLfs(); }}><Box size={15} /><span><strong>Git LFS</strong><small>{isGerman ? "Große Dateien und LFS-Installation verwalten" : "Manage large files and LFS installation"}</small></span></button>
           </div>
         {/if}
       </div>