feat: add porcelain worktree parser with listWorktrees and parseWorktreeListPorcelain

Introduce git worktree list --porcelain parsing following upstream opencode patterns. Exports listWorktrees() for full worktree enumeration with branch info alongside existing detectWorktreePath().

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/start-work/worktree-detector.ts

@@ -1,5 +1,68 @@
 import { execFileSync } from "node:child_process"
 
+export type WorktreeEntry = {
+  path: string
+  branch: string | undefined
+  bare: boolean
+}
+
+export function parseWorktreeListPorcelain(output: string): WorktreeEntry[] {
+  const lines = output.split("\n").map((line) => line.trim())
+  const entries: WorktreeEntry[] = []
+  let current: Partial<WorktreeEntry> | undefined
+
+  for (const line of lines) {
+    if (!line) {
+      if (current?.path) {
+        entries.push({
+          path: current.path,
+          branch: current.branch,
+          bare: current.bare ?? false,
+        })
+      }
+      current = undefined
+      continue
+    }
+
+    if (line.startsWith("worktree ")) {
+      current = { path: line.slice("worktree ".length).trim() }
+      continue
+    }
+
+    if (!current) continue
+
+    if (line.startsWith("branch ")) {
+      current.branch = line.slice("branch ".length).trim().replace(/^refs\/heads\//, "")
+    } else if (line === "bare") {
+      current.bare = true
+    }
+  }
+
+  if (current?.path) {
+    entries.push({
+      path: current.path,
+      branch: current.branch,
+      bare: current.bare ?? false,
+    })
+  }
+
+  return entries
+}
+
+export function listWorktrees(directory: string): WorktreeEntry[] {
+  try {
+    const output = execFileSync("git", ["worktree", "list", "--porcelain"], {
+      cwd: directory,
+      encoding: "utf-8",
+      timeout: 5000,
+      stdio: ["pipe", "pipe", "pipe"],
+    })
+    return parseWorktreeListPorcelain(output)
+  } catch {
+    return []
+  }
+}
+
 export function detectWorktreePath(directory: string): string | null {
   try {
     return execFileSync("git", ["rev-parse", "--show-toplevel"], {