refactor: extract git worktree parser from atlas hook

src/shared/git-worktree/index.ts

@@ -0,0 +1,5 @@
+export type { GitFileStatus, GitFileStat } from "./types"
+export { parseGitStatusPorcelain } from "./parse-status-porcelain"
+export { parseGitDiffNumstat } from "./parse-diff-numstat"
+export { collectGitDiffStats } from "./collect-git-diff-stats"
+export { formatFileChanges } from "./format-file-changes"