Add copilot-hud plugin

[griches]

What

Adds copilot-hud as an external-source plugin entry in marketplace.json.

Why

copilot-hud is a real-time status HUD for the GitHub Copilot CLI's statusLine (experimental) feature. It renders a compact multi-line view with project path, git branch, a live context-window bar (using current_context_used_percentage / displayed_context_limit), running and completed tool activity, background agent tracking, and a remote-session indicator that lights up when a remote controller is attached via `--remote` / `--connect`.

[Opus 4.6 3x·high] │ ◉ remote │ my-project │ git:(main* ↑2) │ ⏱ 5m │ +42/-3
Ctx ████░░░░░░ 70.0k/200.0k 35% │ Reqs 3 │ in:1.5M out:12.2k cache:1.4M │ 42 tok/s
✓ ✎ Edit: auth.ts | ✓ ⌨ Bash: git status ×3 | ◐ ◉ Read: index.ts

Plugin metadata

• Repo: https://github.com/griches/copilot-hud
• License: MIT
• Version: 1.2.5
• Author: Gary Riches
• Latest release: https://github.com/griches/copilot-hud/releases/tag/v1.2.5

Schema notes

Entered as an external source: { source: github, repo: griches/copilot-hud } — same pattern used by the existing fabric-* entries. The plugin lives at the repo root (no path needed). Plugin's own plugin.json declares commands/ and hooks.json.

Happy to adjust the entry, split it differently, or vendor any portion in-tree if the format isn't what you'd like.