docs: add AI-integration section + quickstart, fix ClaudeHAX plugin references

[btopro]

Summary

Consolidates HAX's AI-integration discovery surface into the create repo as part of the PRAW marketplace consolidation.

README.md

• New AI integration section placed right after "Bundled Agent Skills".
• Shows both install paths in one block:
  • Warp / Oz / any agent: hax skills install --all
  • Claude Code: /plugin marketplace add haxtheweb/praw then /plugin install hax-onboarding@haxtheweb
• Golden path: hax site my-hax-site --y --no-i → cd my-hax-site && hax serve → open the local URL.
• Brief notes on the three PRAW plugins (hax-onboarding, hax-site-ops, openstax2hax).

AGENTS.md

• Prominent Quickstart for new users block after the overview, before Setup Commands.
• Notes that Codex reads AGENTS.md natively (Codex onboarding path); Claude Code users can also use the PRAW onboarding plugin.

src/skills/hax-claudehax/SKILL.md

• Plugin-install references updated from the old claudehax marketplace / hax@claudehax to the PRAW marketplace (haxtheweb/praw) and the renamed hax-site-ops plugin (resolves the name collision).
• Repo reference updated to the new marketplace home https://github.com/haxtheweb/praw.
• dist/ untouched — regenerates on next release.

Validation

• README and AGENTS.md markdown renders correctly (verified via diff).
• SKILL.md references now match the canonical install string; no stale claudehax marketplace / hax@claudehax plugin-install references remain.

Draft — part of the PRAW AI-integration consolidation.

Co-Authored-By: Warp agent@warp.dev