Two more TestBackend render tests on top of the connecting/populated/empty set:
- render_stalled_pane_shows_warning_icon — covers the distinct stalled branch
(state_icon → ⚠), which the healthy-Working test (●) didn't exercise.
- render_does_not_panic_on_tiny_terminal — renders at 20x5 to guard against
cramped-layout panics (a classic ratatui footgun).
10 tests pass; fmt clean.
Closes the 'compiles but never verified to draw' gap:
- render_connecting_state_shows_connecting_text — asserts 'connecting…'
and 'colibri-harness' title render before daemon connects
- render_with_snapshot_shows_panes_and_agent — asserts pane id, agent
name, state label, and state icon appear in rendered buffer
- render_does_not_panic_on_empty_snapshot — smoke test for the
snapshot=None path
All three use ratatui::TestBackend (no terminal needed, CI-friendly).
