feat(hud): smart context bar visualization (Wave 2-E)

[JeremyDev87]

Compact visual progress bar for context-window usage: [████░░░░░░] 42%. Danger glyph + ⚠ suffix at thresholds. 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.