feat: GitHub Action for PR suggestions (NEX-001)

[flyingrobots]

Summary

Composite GitHub Action that runs git mind suggest on PRs and posts formatted suggestions as a comment.

Scope

New files

• action.yml — Composite action definition
• action/post-comment.js — Formats JSON → markdown, posts via gh API (~60 LoC)
• .github/git-mind.yml.example — Example config

Design

• No source changes — action consumes existing git mind suggest --json CLI
• Composite action: Setup Node.js 22, npm ci, run suggest, post comment
• Config via .github/git-mind.yml

Test strategy

• No vitest (shell-based action)
• Manual workflow dispatch test

Part of NEXUS milestone.