feat(cli): renderer design system — DESIGN.md spec + ui.ts primitives

[cdot65]

Summary

First half of the output-consistency work. Adds a written design spec (src/cli/renderer/DESIGN.md) and ui primitives that renderers will adopt in the follow-up migration (#268).

Design decisions (per spec)

• One color + glyph per semantic: ✓ green success, ✗ red error, ⚠ yellow warn, ℹ cyan info, ○ skip, ● detection/flag, • neutral
• Headers: bold, no per-module color
• stdout = data; stderr = status/progress/errors (ui.status) so --output json | jq always parses
• Canonical table = existing formatOutput box-drawing style
• No manual isTTY — chalk v5 handles TTY/NO_COLOR

Testing

• 9 new unit tests (ANSI-stripped structure assertions); 652/652 total; lint + tsc clean
• No behavior change to existing commands yet

Checklist

• Spec committed before implementation
• TDD
• Changeset (minor)

Closes #267