feat(external-tools): add cross-platform external tool discovery

Adds a new external tools subsystem to detect and launch
diff and editor tools across Windows, macOS, and Linux.
It exposes data models for tools, commands, and results to the UI
and serializes them for consumption by the app.

- Implement cross-platform discovery of editors and diff tools
- Expose serialized results to the UI for user selection
- Centralize per-OS known tool lists and overrides

src-tauri/src/main.rs

@@ -1,28 +1,33 @@
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
 
 mod badge;
+mod external_tools;
 mod git;
 mod telemetry;
 
 use badge::set_sync_badge;
+use external_tools::{
+    detect_external_tools, launch_external_diff, launch_external_merge, launch_external_tool,
+};
 use git::{
     SearchCancellationState, add_remote, add_worktree, amend_commit, apply_file_patch,
     cancel_code_search, cancel_file_history, checkout_branch, cherry_pick_abort,
     cherry_pick_commit, cherry_pick_continue, clone_repository, commit, commit_ai_generate,
     commit_ai_load, commit_ai_local_models, commit_ai_review, commit_ai_split, commit_ai_status,
     compare_commits, compare_file_to_head, compare_file_to_parent, create_branch, create_tag,
-    cred_delete, cred_load, cred_save, delete_branch, delete_remote_branch, delete_tag,
-    diff_file_against_working_tree, fetch, get_file_blame, get_file_patch, get_remote_url,
-    get_status, init_repository, last_commit_message, list_branches, list_commits,
-    list_file_history, list_interactive_rebase_commits, list_reflog, list_remotes,
-    list_repository_files, list_stashes, list_tags, list_worktrees, lock_worktree, merge_abort,
-    merge_branch, merge_continue, move_worktree, open_repo_in_explorer, open_repository,
-    open_repository_bundle, open_repository_file, prune_worktrees, pull, push, push_tag,
-    read_conflict, rebase_abort, rebase_branch, rebase_continue, remove_remote, remove_worktree,
-    rename_branch, repair_worktree, resolve_conflict, resolve_conflict_side,
-    restore_file_from_commit, restore_files, restore_reflog_entry, restore_to_commit,
-    revert_commit, run_sequence_editor_if_requested, search_code_introductions,
-    set_branch_upstream, stage_files, start_interactive_rebase, stash_apply, stash_drop, stash_pop,
+    cred_delete, cred_load, cred_save, delete_branch, delete_commit_note, delete_remote_branch,
+    delete_tag, diff_file_against_working_tree, fetch, fetch_commit_notes, get_commit_note,
+    get_file_blame, get_file_patch, get_remote_url, get_status, init_repository,
+    last_commit_message, list_branches, list_commits, list_file_history,
+    list_interactive_rebase_commits, list_reflog, list_remotes, list_repository_files,
+    list_stashes, list_tags, list_worktrees, lock_worktree, merge_abort, merge_branch,
+    merge_continue, move_worktree, open_repo_in_explorer, open_repository, open_repository_bundle,
+    open_repository_file, prune_worktrees, pull, push, push_commit_notes, push_tag, read_conflict,
+    rebase_abort, rebase_branch, rebase_continue, remove_remote, remove_worktree, rename_branch,
+    repair_worktree, resolve_conflict, resolve_conflict_side, restore_file_from_commit,
+    restore_files, restore_reflog_entry, restore_to_commit, revert_commit,
+    run_sequence_editor_if_requested, search_code_introductions, set_branch_upstream,
+    set_commit_note, stage_files, start_interactive_rebase, stash_apply, stash_drop, stash_pop,
     stash_push, undo_last_commit, unlock_worktree, unstage_files, update_remote,
 };
 use tauri::Manager;
@@ -123,6 +128,10 @@ async fn main() {
             clone_repository,
             open_repo_in_explorer,
             open_repository_file,
+            detect_external_tools,
+            launch_external_tool,
+            launch_external_diff,
+            launch_external_merge,
             get_status,
             list_branches,
             list_remotes,
@@ -174,6 +183,11 @@ async fn main() {
             push,
             fetch,
             list_commits,
+            get_commit_note,
+            set_commit_note,
+            delete_commit_note,
+            fetch_commit_notes,
+            push_commit_notes,
             restore_to_commit,
             restore_file_from_commit,
             merge_branch,