feat: add experimental tree command with agent index

[kanoru3101]

What/Why/How?

Adds the experimental tree command: it turns an API description into a navigable index, so a human can see its structure and an agent can work with a description far larger than a context window.

redocly tree openapi.yaml                                              # overview: servers, security, tags, webhooks, component sections
redocly tree openapi.yaml --find "create subscription"                 # search operations and components
redocly tree openapi.yaml --path=/orders --operation=post --with-deps  # one operation plus its transitive $ref closure
redocly tree openapi.yaml --component=schemas --name=Order --used-by   # impact analysis: what breaks if this changes

Selection is typed — --tag, --path, --webhook, --operation, --component + --name, --file, plus the standalone --find and --pointer — so there is no id syntax to learn. Every result carries its defining file and line range, so any answer can be checked against the source.

Three formats: stylish for a terminal, json for tooling, and ai — plain text for agents, where every view ends with a next: line naming the flags that continue from it, so an agent runs the whole chain from the output alone without reading any documentation.

The engine is a new api-graph module in @redocly/openapi-core: one walk of the resolved files (the lint pattern, no bundling) builds the dependency graph and index metadata, and the CLI renders views over it. It lives in core because the CLI is one of several planned surfaces. Everything is deterministic — no AI calls, no keys.

Scope: OpenAPI 2.0–3.2. AsyncAPI and Arazzo render their $ref graph; the typed selectors are OpenAPI-only for now.

Measured: 360 agent runs, six tasks over six descriptions from 41 KB to 2,909 files, three models, with and without the index — Where the index pays.

Docs

Reference

• Based on the tree draft (feat(cli): add tree command #2869)

Testing

• Core api-graph unit tests — graph building, selection lookups, views, used-by reports with via chains, deps closure, pointer resolution, webhook classification, path normalization, split-alias canonical ids.
• CLI tree unit tests — selector routing including every invalid combination, and printers asserted against exact strings.
• E2e — every view and format, including the agent loop on a split multi-file fixture, webhook cards, pointer navigation, and the selector-error path with an exit-code assertion.
• Docs examples are captured real CLI output, checked against the command on every change.

Screenshots (optional)

Check yourself

• This PR follows the contributing guide
• All new/updated code is covered by tests
• Core code changed? - Tested with other Redocly products (internal contributions only)
• New package installed? - Tested in different environments (browser/node)
• Documentation update has been considered

Security

• The security impact of the change has been considered
• Code follows company security practices and guidelines