refactor(build,ci): 현재 상태 검증을 걷어내고 불변조건만 남기는 검증 표면 축소

외부 리뷰("현재 상태를 유지하기 위한 검증이 너무 많고, 그 검증 자체를
다시 검증하는 구조까지 생겼다")를 설계 문서로 정리하고 코드로 반영한다.
설계·판단 근거는 docs/superpowers/specs/2026-09-16-verification-surface-reduction-design.md.

삭제
- .github/ci-gate-matrix.yml(1,025줄) + verify-gate-matrix.sh(568줄):
  Gradle task graph와 workflow graph에 이미 있는 정보의 3중 복제
- verify-gradle-wrapper.sh(799줄): workflow 바이트 해시 잠금.
  wrapper 검증은 gradle/actions/wrapper-validation(full SHA 핀)에 위임
- DeveloperExperienceContractTest 등의 CI YAML mutation 테스트:
  애플리케이션 test suite가 GitHub Actions YAML 파서를 검증하던 계층 역전
- 문서 drift 파서: verifyReadmeCommands, verifyRunbookReferences,
  verifyDocumentedLeafCount, verifyTestSourceSetRegistry
- 빈 레지스트리를 지키던 커스텀 YAML 파서: verifyTrivyignore,
  verifyQuarantineSunset, flaky-quarantine.yaml
- verifyConfigurationPropertiesProcessor, verifyOneTypePerFile:
  각각 ca.spring-config convention과 Checkstyle OneTopLevelClass가 대체
- 정상 입력으로도 성공할 수 없던 messaging always-fail task
- ModuleRegistry의 JSON 필드 집합 정확 일치, sample-portfolio negative guard

이동
- java/quality/spring 공통 설정을 configure(subprojects) 블록에서
  ca.java-conventions / ca.quality-conventions / ca.java-library /
  ca.spring-library convention plugin으로
- 아키텍처 검증을 ca.architecture로, JPA·messaging qualification을
  gradle/qualification/ 아래로, verifyEnvKeys를 :app-bootstrap 소유로

완화
- Git revision은 releaseCheck·아카이브 생성에서만 요구. 일반 빌드는 SNAPSHOT
- SpotBugs/FindSecBugs는 로컬 check에서 빼고 qualityCheck 레인으로

task 계층
- leaf check는 그 leaf만. architectureCheck / qualityCheck /
  configContractCheck / integrationCheck / ci / releaseCheck로 이름 분리

CI
- _reusable-gradle.yml 신규. checkout + wrapper validation + JDK/캐시 공통화
- fileserver-release.yml -> fileserver-certification.yml (CD가 아니라 certification)
- GitHub Actions = CI + artifact, Argo CD = CD 경계를 docs/ci-cd/boundary.md로 고정

순증감 +3,274 / -7,483.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/_reusable-gradle.yml

@@ -0,0 +1,63 @@
+name: reusable-gradle
+
+# One place that knows how a Gradle job starts.
+#
+# Every job in this repository opened with the same preamble: checkout, a three-line pinned
+# wrapper-validation step, then the JDK/cache action. The wrapper step is gone (setup-gradle
+# validates wrappers itself), and this workflow removes the rest of the repetition for the jobs whose
+# only variation is the Gradle command they run.
+#
+# Jobs that need service containers, a matrix, artifact uploads or per-job env stay written out with
+# `./.github/actions/setup-gradle-java`, because expressing those through `workflow_call` inputs
+# means encoding YAML inside strings — which is how a "shared" workflow becomes less readable than
+# the duplication it replaced.
+
+on:
+  workflow_call:
+    inputs:
+      tasks:
+        description: The Gradle task list, whitespace-separated.
+        required: true
+        type: string
+      gradle-args:
+        description: Flags appended after the task list.
+        required: false
+        type: string
+        default: "--no-daemon --stacktrace"
+      working-directory:
+        description: Directory the wrapper is invoked from.
+        required: false
+        type: string
+        default: src
+      timeout-minutes:
+        required: false
+        type: number
+        default: 30
+      continue-on-error:
+        description: Run the job as an advisory signal rather than a gate.
+        required: false
+        type: boolean
+        default: false
+
+permissions:
+  contents: read
+
+jobs:
+  gradle:
+    runs-on: ubuntu-latest
+    timeout-minutes: ${{ inputs.timeout-minutes }}
+    continue-on-error: ${{ inputs.continue-on-error }}
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # actions/checkout@v4.2.2
+      - uses: ./.github/actions/setup-gradle-java
+      - name: Run ${{ inputs.tasks }}
+        working-directory: ${{ inputs.working-directory }}
+        env:
+          GRADLE_TASKS: ${{ inputs.tasks }}
+          GRADLE_ARGS: ${{ inputs.gradle-args }}
+        run: |
+          set -euo pipefail
+          # Word-split on purpose: both inputs are task/flag lists. They come from this repository's
+          # own workflow files, never from a pull request.
+          # shellcheck disable=SC2086
+          ./gradlew ${GRADLE_TASKS} ${GRADLE_ARGS}