Surface native agent input requests

Review fixes: re-check ownership before a write that awaited

Re-pin: a session's folder is a tree, not one directory

Pin Claude, Codex, and OpenCode conversations from lifecycle events (#41)

Repin: don't let a relaunch mid-scan leave two watchers

Repin: await the transcript scan, and shorten the backstop to a minute

Repin: fix the pane root, then stop scanning the bucket every 20s

Sessions: let the pane say which conversation it is on (#23)

Sessions: follow the conversation when a harness starts a new one (#17)