fix(starter): bundle springdoc — Swagger UI from the starter alone (0.2.1)

[jlc488]

What / 무엇

Makes Swagger UI come up from the starter alone — bundle springdoc in the starter so the kit's "add the starter, nothing else" promise covers the API docs too. Ships as 0.2.1.

Swagger UI가 스타터만으로 뜨도록 — springdoc을 스타터에 포함해 "스타터만 추가하면 다 됨" 약속을 API 문서까지 확장. 0.2.1로 배포.

Why / 왜

0.2.0 shipped springdoc as compileOnly, so OpenApiAutoConfiguration only activated if the consumer added springdoc themselves — Swagger UI did not appear from the starter alone. That contradicts the kit's whole premise.

0.2.0은 springdoc을 compileOnly로 배포 → 소비자가 직접 추가해야만 Swagger UI가 떴음. 킷 철학과 어긋남.

How / 어떻게

• starter — adds api("org.springdoc:springdoc-openapi-starter-webmvc-ui"), so it reaches the consumer's classpath transitively; @ConditionalOnClass(GroupedOpenApi) trips and /swagger-ui + /v3/api-docs serve out of the box.
• autoconfigure — keeps its compileOnly springdoc + @ConditionalOnClass, so it still compiles/stays dormant without springdoc; the starter guarantees presence.
• sample-app — removes its own springdoc dependency, so the OpenAPI tests now prove Swagger works from the starter's transitive springdoc alone (the real "starter only" path).
• opt-out (documented): devslab.kit.openapi.enabled=false (keep jar, disable surface) or exclude the org.springdoc dependency (drop the jar) — Gradle + Maven snippets in the config reference.

Verification / 검증

Full ./gradlew clean build green — 44 tests, 0 failures, with no springdoc declared in sample-app: OpenApiEndpointTests 3/3 (/v3/api-docs 200+valid JSON, admin group, /swagger-ui 200) + OpenApiDisabledTests 1/1. mkdocs --strict clean.

Docs / 문서

README(.ko) Features + Config, docs/reference/configuration(.ko) reworded with exclude snippets, CHANGELOG(.ko) [0.2.1], install coordinates → 0.2.1.

Merge → tag v0.2.1 → Maven Central. (0.2.0 is already published; this is the patch that actually delivers auto-Swagger.)