cli: terminal output as screens #316

Terminal output drawn as magit-style screens: a header block of Label: lines, a body, counted sections in bold blue, and a legend of the commands that apply. Refs dim instead of cyan, one glyph per state (✓ ✗ ◐ ● ○), no header rows. Piped and --json output unchanged; all rendering stays server-side behind --term.

Spec: docs/specs/2026-10-01-cli-views-design.md Plan (stages 1 and 2): docs/plans/2026-10-01-cli-views.md

Stages, merged in order:

1. Renderer: screen, emitView, legend, here= from the CLI; table restyled.
2. Show screens (mr show, issue show, repo show, build show), then lists (mr list, issue list, build list) and dashboard.
3. Every other c.table / c.view caller; view's terminal branches removed. Planned after stage 2 lands.

Stages: #317 (renderer), #318 (show, list and dashboard screens), #319 (remaining commands).