docs: add PR and documentation guidance

[rlippmann]

Summary

Add commit/PR naming guidance and documentation-process guidance to AGENTS.md.

Why

Future agent-driven commits and PRs should use consistent conventional prefixes and the repository PR template. This also brings over a few documentation rules from context-compiler that fit this example-integrations repository, especially around treating example docs as part of the project contract.

Example metadata

• Enforcement point: repository governance and documentation process
• Domain: repository maintenance
• Technology/runtime: documentation
• Example type: repository maintenance
• Does this use directive drafter? should normally be no: no
• Does this derive state from model output? must be no for primary examples: no

Checklist

• Repository scaffolding / governance change
• One primary enforcement point
• Explicit authoritative state
• No model-derived state mutation
• Adversarial stub or equivalent test
• Observable runtime behavior change
• Domain vocabulary is natural
• Framework is secondary to the enforcement point
• Docs updated
• Tests/smoke checks added where practical

Notes

This is a docs-only update to repository guidance. No code, examples, or tests changed.