fix: add GitContext type annotation to mock in generate.test.ts

The mockGitContext variable was declared without a type annotation,
causing TypeScript to infer a narrow type from the initial assignment
(status: "modified"). This made reassignment with status: "added"
fail with TS2322. Adding the GitContext type allows all valid status
values.

packages/opencode/src/commit-message/__tests__/generate.test.ts

@@ -1,8 +1,9 @@
 import { describe, expect, test, mock, beforeEach } from "bun:test"
+import type { GitContext } from "../types"
 
 // Mock dependencies before importing the module under test
 
-let mockGitContext = {
+let mockGitContext: GitContext = {
   branch: "main",
   recentCommits: ["abc1234 initial commit"],
   files: [