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/types.ts

@@ -9,9 +9,7 @@ export type FileStatusKind =
 
 export type GitIgnoreKind = "file" | "extension" | "folder";
 
-export type CommitAiPhase = "idle" | "loading" | "ready" | "error";
-export type CommitAiProvider = "local" | "openai" | "anthropic" | "custom";
-export type CommitAiLocalProfile = "fast" | "balanced" | "detailed";
+export type CommitAiProvider = "openai" | "anthropic" | "custom";
 export type AppTheme = "system" | "light" | "dark";
 export type AppAppearance = "modern" | "classic" | "custom";
 export type AppLanguage = "en" | "de";
@@ -74,12 +72,6 @@ export interface CustomThemeColors {
   text: string;
 }
 
-export interface CommitAiStatus {
-  phase: CommitAiPhase;
-  model_id: string | null;
-  error: string | null;
-}
-
 export type AiReviewRisk = "low" | "medium" | "high";
 export type AiReviewSeverity = "critical" | "warning" | "info";
 
@@ -109,16 +101,8 @@ export interface AiCommitPlan {
   groups: AiCommitGroup[];
 }
 
-export interface LocalModelOption {
-  id: string;
-  label: string;
-  approx_size_mb: number;
-}
-
 export interface AiSettings {
   provider: CommitAiProvider;
-  localModelId: string;
-  localProfile: CommitAiLocalProfile;
   openaiModel: string;
   anthropicModel: string;
   customBaseUrl: string;