feat(ai): add AI-assisted commit splitting flow

Introduce a split-planning path for staged changes that asks supported AI
providers to group files into ordered Conventional Commit messages. The
plan is validated before execution so every staged file is assigned once
and unsafe states are rejected.

A new dialog lets users review and adjust the proposed groups before
creating the commits in sequence, with safeguards to preserve remaining
changes if something fails.

src/lib/types.ts

@@ -37,6 +37,17 @@ export interface AiReviewResult {
   findings: AiReviewFinding[];
 }
 
+export interface AiCommitGroup {
+  message: string;
+  reason: string;
+  files: string[];
+}
+
+export interface AiCommitPlan {
+  summary: string;
+  groups: AiCommitGroup[];
+}
+
 export interface LocalModelOption {
   id: string;
   label: string;