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/index.ts

@@ -1,4 +1,4 @@
 export { HOOK_NAME, createStartWorkHook } from "./start-work-hook"
-export { detectWorktreePath } from "./worktree-detector"
+export { detectWorktreePath, listWorktrees, parseWorktreeListPorcelain } from "./worktree-detector"
 export type { ParsedUserRequest } from "./parse-user-request"
 export { parseUserRequest } from "./parse-user-request"