6654: Replace API spec workflow with oasdiff-based breaking change detection

Replace the old api-spec.yml (Java-based openapitools/openapi-diff, task runner)
with a new api-spec.yaml using oasdiff (Go, FOSS). Fixes file name mismatch
(spec.yaml -> api-spec-v1.yaml), uses docker compose pattern, and adds path
filtering. Remove redundant apispec job from pr.yaml.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: turegjorup

.github/workflows/api-spec.yaml

@@ -0,0 +1,141 @@
+name: API Specification
+
+on:
+  pull_request:
+    paths:
+      - "src/**/*.php"
+      - "config/**"
+      - "composer.json"
+      - "composer.lock"
+      - "public/api-spec-v1.yaml"
+      - "public/api-spec-v1.json"
+      - "docker-compose.yml"
+
+env:
+  COMPOSE_USER: runner
+
+jobs:
+  api-spec-export:
+    name: Ensure API specification is up to date
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Create docker network
+        run: docker network create frontend
+
+      - name: Export API specification
+        run: |
+          docker compose up --detach
+          docker compose exec phpfpm composer install --no-interaction
+          docker compose exec phpfpm composer update-api-spec
+
+      - name: Check for uncommitted changes
+        id: git-diff-spec
+        continue-on-error: true
+        run: |
+          git diff --diff-filter=ACMRT --exit-code public/api-spec-v1.yaml public/api-spec-v1.json
+
+      - name: Comment PR if spec is outdated
+        if: steps.git-diff-spec.outcome == 'failure'
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh pr comment ${{ github.event.pull_request.number }} \
+            --body "$(cat <<'EOF'
+          ## API specification not up to date
+
+          The committed API specification files do not match the exported output.
+
+          Please run the following command, then commit and push the changes:
+
+          ```shell
+          docker compose exec phpfpm composer update-api-spec
+          ```
+          EOF
+          )" \
+            --create-if-none --edit-last
+
+      - name: Fail if spec is outdated
+        if: steps.git-diff-spec.outcome == 'failure'
+        run: exit 1
+
+  api-spec-breaking-changes:
+    name: Detect breaking changes in API specification
+    runs-on: ubuntu-latest
+    needs: [api-spec-export]
+    permissions:
+      pull-requests: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Fetch base branch for comparison
+        run: git fetch --depth=1 origin ${{ github.base_ref }}
+
+      - name: Detect breaking changes
+        id: breaking
+        continue-on-error: true
+        uses: oasdiff/oasdiff-action/breaking@main
+        with:
+          base: 'origin/${{ github.base_ref }}:public/api-spec-v1.yaml'
+          revision: 'public/api-spec-v1.yaml'
+          fail-on: ERR
+
+      - name: Generate changelog
+        id: changelog
+        continue-on-error: true
+        uses: oasdiff/oasdiff-action/changelog@main
+        with:
+          base: 'origin/${{ github.base_ref }}:public/api-spec-v1.yaml'
+          revision: 'public/api-spec-v1.yaml'
+          format: markdown
+          output-to-file: changelog.md
+
+      - name: Comment PR - no changes
+        if: steps.breaking.outcome == 'success' && hashFiles('changelog.md') == ''
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh pr comment ${{ github.event.pull_request.number }} \
+            --body "## API Specification
+
+          No changes detected in API specification." \
+            --create-if-none --edit-last
+
+      - name: Comment PR - non-breaking changes
+        if: steps.breaking.outcome == 'success' && hashFiles('changelog.md') != ''
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          {
+            echo "## API Specification - Non-breaking changes"
+            echo ""
+            cat changelog.md
+          } > comment.md
+          gh pr comment ${{ github.event.pull_request.number }} \
+            --body-file comment.md \
+            --create-if-none --edit-last
+
+      - name: Comment PR - breaking changes
+        if: steps.breaking.outcome == 'failure'
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          {
+            echo "## API Specification - Breaking changes detected"
+            echo ""
+            if [ -s changelog.md ]; then
+              cat changelog.md
+            else
+              echo "The breaking changes action detected incompatible changes. Review the action logs for details."
+            fi
+          } > comment.md
+          gh pr comment ${{ github.event.pull_request.number }} \
+            --body-file comment.md \
+            --create-if-none --edit-last
+
+      - name: Fail if breaking changes detected
+        if: steps.breaking.outcome == 'failure'
+        run: exit 1