Docs: Add Moxie agent guidance

[moxie-docs]

What Moxie is changing

This PR keeps repository-level agent guidance current so Codex, Cursor, Claude, and other coding agents use Moxie's live MCP context before editing.

• AGENTS.md holds a short, always-on pointer to the Moxie Docs MCP server and the moxie-docs skill.
• .claude/skills/moxie-docs/SKILL.md and .agents/skills/moxie-docs/SKILL.md add a triggered skill describing the edit-then-document workflow. It reads conventions, verified commands, and gaps live from the MCP server, so it stays correct without churn as your codebase changes.

Why this helps

• Agents get repo conventions, docs patterns, gaps, and verified commands on demand instead of re-crawling the repo.
• Feature work gets a clear docs expectation without forcing filler documentation.
• The skill is generated from your repo slug only; it re-opens a PR like this one only on a rename or a Moxie workflow update, not on every convention change.

Source paths

• AGENTS.md
• README.md
• backend/README.md
• frontend/src/App.js

[moxie-docs]

Moxie Docs — documentation findings

Moxie spotted documentation gaps that line up with the files this PR changes. This is a warning, not a blocker.

• API behavior needs reader-facing documentation — touches AGENTS.md
  Missing explicit notes on how backend and frontend behavior contract is enforced and how to extend.

• Testing strategy is hard to infer from file inventory — touches AGENTS.md
  Tests exist but lack documentation on testing scope, how to run, and what is expected.

Fix with Moxie

Paste this into Claude Code (or any MCP-aware client) connected to the Moxie Docs MCP:

Update the docs for PR #3 in Jackalope-Dev/fullstack-app-example. Use the moxie-docs MCP:
- `moxie_get_doc_gaps` to see which gaps this PR touches
- `moxie_search_docs` to find the right pages to edit
- `moxie_get_documentation_patterns` to match repo conventions
- `moxie_get_documentation_opportunities` to confirm what's worth shipping

See the full picture on the Moxie overview.