feat(page): DocsUI::RequestExample + JsonResponse — one request definition, every client tab

[mhenrixon]

Closes #15.

Problem

An endpoint example was authored 5–7 times — curl, CLI, JavaScript, Ruby, Python heredocs (one builder method per client per endpoint), plus a hand-pretty-printed JSON response with deep_stringify copy-pasted 3×. A field rename meant editing up to 7 places. The gem's Example was just a tab container; there was no way to define a request once and derive the language tabs.

What this ships

One structured request declaration renders every configured client tab; one Ruby hash renders a pretty JSON response block.

DocsUI::Section("Create a payment link",
  description: DocsUI::Endpoint.new(:post, "/v1/payment_links")) do

  render DocsUI::RequestExample.new(
    method: :post, path: "/v1/payment_links",
    body: { amount: 4900, currency: "usd", description: "Pro plan" }
  )
  render DocsUI::JsonResponse.new(
    { id: "plink_1a2b3c", object: "payment_link", amount: 4900, currency: "usd" }
  )
end

Value objects (lib/docs_kit/)

• DocsKit::ApiRequest (Data.define) — method/path/url/query/headers/body, plus derived #http_method, #body?, #pretty_body_json (deep-stringified), #url_with_query. This is what templates receive, so each stays one short heredoc.
• DocsKit::ApiClient (Data.define) — label/lexer/filename (String or proc)/template ((request) -> String). Ships four generic-HTTP defaults (curl, javascript, ruby, python) in ApiClient::DEFAULTS, backed by DocsKit::ApiTemplates.

Config (all defaulted — backwards compatible)

Knob	Default	Purpose
c.api_clients	the four defaults	Ordered { token => ApiClient } merged over the defaults — reuse a token to swap in an SDK-flavored snippet, new token to append a tab (e.g. cli). Order stable.
c.api_base_url	"https://api.example.com"	Prefixed onto each request path.
c.api_auth_header	nil	Example Authorization: line merged into every snippet; nil ⇒ no auth line.

Components (app/components/docs_ui/)

• DocsUI::JsonResponse.new(body, filename: "response.json") — Hash → deep-stringified + JSON.pretty_generate; String → passthrough; renders DocsUI::Code(lexer: :json).
• DocsUI::RequestExample.new(method:, path:, body:, query:, headers:, clients:) — composes DocsUI::Example, one tab per selected client, so the global sticky language preference keeps working. clients: filters/orders the tabs.
• DocsUI::Example#code gains an optional label: (additive — existing behavior unchanged) so a client carries its own tab name.

The gem ships generic HTTP templates only — it can't know a site's SDK. app-4's SDK flavors and its cli tab become c.api_clients overrides.

Test coverage

• api_request_spec — derived helpers; deep-stringify across Hash/Array/Symbol; query encoding; String passthrough.
• api_client_spec — value object + filename_for (String/proc); the four default templates asserting body-present vs body-less GET, and the auth-header line.
• configuration_spec — api_clients defaults/order/merge/override; api_base_url/api_auth_header defaults + overrides.
• json_response_spec — Hash pretty-print with string keys, String passthrough, HTML-escape safety via the Rouge path.
• request_example_spec — a POST renders 4 tabs; curl carries api_base_url+method+-d body; auth header injected; clients: [:ruby, :curl] filters and orders; a custom client from config renders its own label; a body-less GET omits payload lines in every default template; Example's progressive-enhancement markup (no server-side hidden panels).

Also smoke-tested the exact dogfood composition (RequestExample + JsonResponse in an endpoint Section) renders clean end-to-end.

Verification

• bundle exec rake (rspec + rubocop) — 232 examples, 0 failures; no offenses
• DocsKit::Configuration still 100% covered; suite 93% line coverage (floor 80%)
• Backwards compatible — DocsUI::Example behavior preserved (additive optional label:), all new config knobs defaulted
• Dogfooded — an "API-docs kit" section on the components page; README "API docs" section

Out of scope (per the issue)

OpenAPI import (the request struct is the stepping stone a bridge would target later); response generation from live serializers; WebSocket/streaming shapes.