feat(hud): mode rainbow ANSI coloring (Wave 2-D)

[JeremyDev87]

Adds per-mode ANSI color + glyph: PLAN ◇ blue, ACT ◆ green, EVAL ◈ purple, AUTO ◊ rainbow. Honours NO_COLOR. Part of #1464.

[JeremyDev87]

Implemented and merged via #1485 (Wave 0-3 integrator) and #1487 (Wave 3b follow-up). Module lives in packages/claude-code-plugin/hooks/lib/. Closing as complete.