argus caught that the previous wording ("splitting a long-lived file
into dated pieces") suggested a remedy that increases top-level entry
count unless the pieces land in a subdirectory - wrong advice for the
exact metric this watch counts.
Also added mara's ask: explicitly note the agent can leave the todo
open and act on it later, no pressure to resolve immediately.
New state_entry_watch.rs, mirroring disk_watch.rs's shape exactly:
periodic in-process probe, Todos::upsert with a stable count-bucketed
summary (anti-nag - drifting inside one bucket stays silent, crossing
a bucket speaks up again), clears once back under threshold.
Top-level entry count only, deliberately - a large subdirectory (git
clone, build tree) counts as one entry regardless of what's inside it,
which is disk_watch's problem to catch on its own axis (bytes), not
this one's.
Wired into main.rs's spawn_todo_socket alongside disk_watch::run.
closes#3464
