feat(docs): publish validated agent discovery

[mattsse]

Summary

• publish a versioned agent-index.json with 14 task intents, retrieval vocabulary, feature flags, configuration requirements, and 185 canonical pages
• rewrite generated llms links to absolute alloy.rs URLs and validate the agent artifacts during every build
• add repository AGENTS.md guidance for source ownership, generated files, endpoint hygiene, and snippet verification
• add CI validation for internal routes, anchors, page descriptions, retired endpoints, sidebar targets, and generated discovery files
• repair stale anchors, one extension-bearing route, missing metadata, and a brittle custom-network endpoint while introducing the checks

Why

The current llms inventory is a flat list with root-relative links, no version fields, and no way to map user intent to required features, environment variables, guides, and examples. Repository agents also lack instructions distinguishing hand-written pages from generated example output. Broken anchors can pass the static-site build unnoticed.

Impact

Agents can start with a compact structured index, retrieve only the pages needed for a task, and verify the target Alloy versions before generating code. CI prevents common discovery regressions, while contributors get explicit ownership and validation rules for documentation and generated content.