refactor: extract git worktree parser from atlas hook

src/shared/git-worktree/collect-git-diff-stats.ts

@@ -0,0 +1,29 @@
+import { execSync } from "node:child_process"
+import { parseGitStatusPorcelain } from "./parse-status-porcelain"
+import { parseGitDiffNumstat } from "./parse-diff-numstat"
+import type { GitFileStat } from "./types"
+
+export function collectGitDiffStats(directory: string): GitFileStat[] {
+  try {
+    const diffOutput = execSync("git diff --numstat HEAD", {
+      cwd: directory,
+      encoding: "utf-8",
+      timeout: 5000,
+      stdio: ["pipe", "pipe", "pipe"],
+    }).trim()
+
+    if (!diffOutput) return []
+
+    const statusOutput = execSync("git status --porcelain", {
+      cwd: directory,
+      encoding: "utf-8",
+      timeout: 5000,
+      stdio: ["pipe", "pipe", "pipe"],
+    }).trim()
+
+    const statusMap = parseGitStatusPorcelain(statusOutput)
+    return parseGitDiffNumstat(diffOutput, statusMap)
+  } catch {
+    return []
+  }
+}