RecoverStuckTasks scans for tasks with updated_at > 5min ago and
re-enqueues them. This incorrectly matched tasks actively being
processed by the worker (e.g. slow downloads), causing
double-processing.
Add inflight sync.Map to track taskIDs currently inside ProcessTask.
RecoverStuckTasks skips tasks found in inflight. On server restart
inflight is empty (in-memory), so genuinely stuck tasks are still
correctly recovered.
Also: increase taskCh buffer 16→10000, add periodic RecoverStuckTasks
goroutine in TaskPoller (every 5min), and add status guard in
ProcessTask as defense-in-depth against duplicate enqueues.
- GetFile uses new GetFileResponse instead of manual FileResponse construction
- ListFiles handler parses optional user_id query parameter
- Wire FolderStore into FileService in app.go, testenv, and file_test
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
