cli: agent rm/show reject the short session ids that agent list prints

[edwin-zvs]

Summary

agent list prints truncated 10-char session ids (e.g. s79aa42b2d), but agent rm / agent show require the full id. Passing the displayed short id fails with a bare "session not found" and no hint.

Repro

$ agent list
● s79aa42b2d  antigravity  awaiting input  ...
$ agent rm s79aa42b2d
Error: daemon error: session not found: s79aa42b2d
$ agent rm s79aa42b2dc0042fe870de8f628db071d   # full id
(ok)

Suggested fix

Accept unique id prefixes in CLI commands (rm/show/send/stop/…), or print full ids in agent list, or add a "did you mean <full-id>?" hint.

Found during an isolated dogfood run.