feat(git stash): add stash listing and push/apply/pop/drop UI

This change introduces Git stash support end-to-end, including a new
backend command to list stashes and operations to push, apply, pop, and
drop them. The frontend now fetches stashes as part of the repository
bundle and provides a dedicated panel to manage shelved changes.

- Add GitStash model and Tauri commands for stash operations
- Implement StashPanel component and wire it into the app
- Adjust sidebar layout and add stash-specific styling

src-tauri/src/main.rs

@@ -10,10 +10,11 @@ use git::{
     commit_ai_status, compare_commits, compare_file_to_head, compare_file_to_parent, create_branch,
     cred_delete, cred_load, cred_save, delete_branch, diff_file_against_working_tree, fetch,
     get_file_patch, get_remote_url, get_status, list_branches, list_commits, list_file_history,
-    list_repository_files, merge_branch, open_repo_in_explorer, open_repository,
+    list_repository_files, list_stashes, merge_branch, open_repo_in_explorer, open_repository,
     open_repository_bundle, open_repository_file, pull, push, read_conflict, rename_branch,
     resolve_conflict, resolve_conflict_side, restore_file_from_commit, restore_files,
-    restore_to_commit, search_code_introductions, stage_files, unstage_files,
+    restore_to_commit, search_code_introductions, stage_files, stash_apply, stash_drop, stash_pop,
+    stash_push, unstage_files,
 };
 
 fn main() {
@@ -28,12 +29,17 @@ fn main() {
             open_repository_file,
             get_status,
             list_branches,
+            list_stashes,
             checkout_branch,
             create_branch,
             rename_branch,
             delete_branch,
             stage_files,
             unstage_files,
+            stash_push,
+            stash_apply,
+            stash_pop,
+            stash_drop,
             restore_files,
             get_file_patch,
             apply_file_patch,