Add cc-hud to Usage & Observability

[WaterTian]

Adds cc-hud, a compact single-line Claude Code statusline.

• Shows model, context usage (1/8-char progress bar), active subagents, 5h/7d rate-limit countdowns
• Install: /plugin marketplace add WaterTian/cc-hud
• npm: cc-hud v0.2.4 (MIT)
• Pure Node.js >=18, zero dependencies, Catppuccin Mocha colors

Fits alongside ccstatusline, cc-statusline, CCometixLine, claude-statusline already in this section.