feat(git): add tag management and cherry-pick workflow

This update extends the Git backend and UI to support listing,
creating, deleting, and pushing tags. It also adds cherry-pick
commands with proper in-progress detection and conflict handling, and
prevents other operations while a cherry-pick is active.

- Add GitTag model, tag listing, and tag CRUD/push commands
- Implement cherry-pick start/continue/abort with status tracking
- Update UI to display tags and gate actions during cherry-pick

src/lib/types.ts

@@ -42,6 +42,7 @@ export interface GitStatus {
   files: GitFileStatus[];
   clean: boolean;
   rebase_in_progress: boolean;
+  cherry_pick_in_progress: boolean;
 }
 
 export interface GitFileStatus {
@@ -59,6 +60,15 @@ export interface GitBranch {
   remote: boolean;
 }
 
+export interface GitTag {
+  name: string;
+  hash: string;
+  short_hash: string;
+  message: string | null;
+  date: string;
+  annotated: boolean;
+}
+
 export interface GitStash {
   selector: string;
   index: number;
@@ -95,6 +105,7 @@ export interface GitRepositoryFile {
 export interface RepositoryBundle {
   status: GitStatus;
   branches: GitBranch[];
+  tags: GitTag[];
   stashes: GitStash[];
   commits: GitCommit[];
   files: GitRepositoryFile[];