test: rename 'fake' test agent → 'sample' (lighter, less loaded)
'fake' carries a broad/negative association. Rename the test-double agent and
all its references to 'sample' (it emits a canned sample of pi-format JSONL):
- scripts/fake-pi-agent.py → scripts/sample-pi-agent.py (git mv, mode kept)
- pi_spawn_live.rs: sample-pi-agent.py, pane label 'sample-pi'
- socket.rs: fn sample_agent_stdout_stream_updates_glasspane, labels, 'pi-sample'
- live_socket_check.rs: sample_agent; colibri.rs: /tmp/sample-agent
- glasspane/spawner doc comments: 'sample JSONL readers'
- docs (ISO-SERVICE-LAYOUT, PRIORITY-HANDOFF, ISO-ACCEPTANCE-RUNBOOK)
Pure rename; no behavior change. ./scripts/ci-checks.sh green.
Stacks on #158.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>