refactor(commit-ai): remove local models and simplify AI flow

Remove local on-device model support and related IPC commands,
consolidating commit-generation to cloud providers and simplifying the
AI crate surface. Local-specific types, generation profiles, caching,
and the local prompt builder were removed while message sanitization and
diff-echo detection were preserved. Also harden repository handling and
runtime: unborn HEADs are handled gracefully so empty repos still report
files, Git LFS sync is skipped for repositories without commits, and
tokio runtime features were enabled.

- Remove local model engine, load/status commands, and local profile code
- Handle unborn HEAD and skip LFS sync for repos without commits
- Enable tokio runtime features and route AI generation to cloud only

src/lib/git.ts

@@ -3,9 +3,7 @@ import { tracedInvoke as invoke } from "./telemetry";
 import type {
   AiReviewResult,
   AiCommitPlan,
-  CommitAiLocalProfile,
   CommitAiProvider,
-  CommitAiStatus,
   ConflictFile,
   DetectedExternalTool,
   ExternalToolCommand,
@@ -30,7 +28,6 @@ import type {
   GitStatus,
   GitTag,
   GitWorktree,
-  LocalModelOption,
   PatchApplyAction,
   RepositoryBundle,
   StoredCredential,
@@ -369,22 +366,9 @@ export function stashDrop(path: string, selector: string): Promise<GitStatus> {
   return invoke<GitStatus>("stash_drop", { path, selector });
 }
 
-export function commitAiStatus(): Promise<CommitAiStatus> {
-  return invoke<CommitAiStatus>("commit_ai_status");
-}
-
-export function commitAiLoad(modelId: string): Promise<void> {
-  return invoke<void>("commit_ai_load", { modelId });
-}
-
-export function commitAiLocalModels(): Promise<LocalModelOption[]> {
-  return invoke<LocalModelOption[]>("commit_ai_local_models");
-}
-
 export interface CommitAiGenerateOptions {
   notes?: string;
   provider: CommitAiProvider;
-  localProfile?: CommitAiLocalProfile;
   model?: string;
   apiKey?: string;
   baseUrl?: string;
@@ -395,7 +379,6 @@ export function commitAiGenerate(path: string, options: CommitAiGenerateOptions)
     path,
     notes: options.notes,
     provider: options.provider,
-    localProfile: options.localProfile,
     model: options.model,
     apiKey: options.apiKey,
     baseUrl: options.baseUrl,