refactor(agentic): route file I/O through core.Fs
Replace raw os.* file operations with Core Fs equivalents:
- os.Stat → fs.Exists/fs.IsFile/fs.IsDir (resume, pr, plan, mirror, prep)
- os.ReadDir → fs.List (queue, status, plan, mirror, review_queue)
- os.Remove → fs.Delete (dispatch)
- os.OpenFile(append) → fs.Append (events, review_queue)
- strings.Replace → core.Replace (scan)
Eliminates os import from resume.go, pr.go. Eliminates strings
import from scan.go. Trades os for io in events.go.
Co-Authored-By: Virgil <virgil@lethean.io>
3022f05fb8