feat(branches): add force delete flow for local branches

Branch deletion now supports an optional force mode in the Tauri
command, enabling deletion of branches that are not fully merged.
The UI replaces the simple confirm prompt with a dedicated dialog and
auto-escalates to force delete when Git rejects a normal delete.

- Add force flag to delete_branch command and tests
- Implement BranchDeleteConfirmDialog and wire it into App.svelte
- Update branch context menu actions and styling

src-tauri/src/git.rs

@@ -530,7 +530,11 @@ pub fn rename_branch(
 }
 
 #[tauri::command]
-pub fn delete_branch(path: String, branch: String) -> Result<GitStatus, String> {
+pub fn delete_branch(
+    path: String,
+    branch: String,
+    force: Option<bool>,
+) -> Result<GitStatus, String> {
     let repo = resolve_repo(&path)?;
     let branch = validate_existing_local_branch_name(&repo, &branch)?;
     let status = status_for_repo(&repo)?;
@@ -538,7 +542,8 @@ pub fn delete_branch(path: String, branch: String) -> Result<GitStatus, String>
         return Err("The current branch cannot be deleted.".to_string());
     }
 
-    run_git(&repo, ["branch", "-d", "--", branch.as_str()])?;
+    let delete_flag = if force.unwrap_or(false) { "-D" } else { "-d" };
+    run_git(&repo, ["branch", delete_flag, "--", branch.as_str()])?;
     status_for_repo(&repo)
 }
 
@@ -4522,8 +4527,12 @@ mod tests {
         let current = git_output_test(&repo.path, ["rev-parse", "--abbrev-ref", "HEAD"]);
         run_git_test(&repo.path, ["branch", "stale"]);
 
-        let status =
-            delete_branch(repo.path.to_string_lossy().to_string(), "stale".to_string()).unwrap();
+        let status = delete_branch(
+            repo.path.to_string_lossy().to_string(),
+            "stale".to_string(),
+            None,
+        )
+        .unwrap();
 
         assert_eq!(status.current_branch.as_deref(), Some(current.as_str()));
         assert!(
@@ -4531,10 +4540,43 @@ mod tests {
             "deleted branch should be gone"
         );
 
-        let err = delete_branch(repo.path.to_string_lossy().to_string(), current).unwrap_err();
+        let err =
+            delete_branch(repo.path.to_string_lossy().to_string(), current, None).unwrap_err();
         assert!(err.contains("current branch"));
     }
 
+    #[test]
+    fn delete_branch_can_force_delete_unmerged_branch() {
+        let repo = init_temp_repo("delete_branch_force");
+        commit_initial_file(&repo.path);
+        let current = git_output_test(&repo.path, ["rev-parse", "--abbrev-ref", "HEAD"]);
+        run_git_test(&repo.path, ["checkout", "-q", "-b", "feature/unmerged"]);
+        fs::write(repo.path.join("feature.txt"), "feature\n")
+            .expect("feature file should be written");
+        run_git_test(&repo.path, ["add", "feature.txt"]);
+        run_git_test(&repo.path, ["commit", "-q", "-m", "feature"]);
+        run_git_test(&repo.path, ["checkout", "-q", current.as_str()]);
+
+        let err = delete_branch(
+            repo.path.to_string_lossy().to_string(),
+            "feature/unmerged".to_string(),
+            Some(false),
+        )
+        .unwrap_err();
+        assert!(err.contains("not fully merged"));
+
+        delete_branch(
+            repo.path.to_string_lossy().to_string(),
+            "feature/unmerged".to_string(),
+            Some(true),
+        )
+        .unwrap();
+        assert!(
+            !ref_exists(&repo.path, "refs/heads/feature/unmerged").unwrap(),
+            "force-deleted branch should be gone"
+        );
+    }
+
     #[test]
     fn apply_file_patch_stages_and_discards_selected_changes() {
         let repo = init_temp_repo("apply_file_patch");