Add GitHub Actions CI and Dependabot (#1)

## Summary
- Add `.github/workflows/ci.yml` — CI workflow with JDK matrix [21, 25],
`ktlintCheck` + `test`, test artifact upload, Dependabot auto-merge
- Add `.github/dependabot.yml` — weekly dependency updates for Gradle
(grouped: production vs testing) and GitHub Actions, with auto-merge via
shared SML workflow

Implements
[KOJAK-34](https://softwaremill.atlassian.net/browse/KOJAK-34).

## Details

**CI workflow:**
- Triggers on push to `main` and PRs
- Matrix: JDK 21 (minimum, `jvmToolchain(21)`) + JDK 25 (latest LTS)
- `fail-fast: false` for full signal on both JDK versions
- `permissions: contents: write` + `pull-requests: write` (required for
auto-merge)
- Third-party actions SHA-pinned (`gradle/actions`), GitHub-owned use
version tags

**Dependabot auto-merge:**
- `auto-merge-dependabot` job calls shared
`softwaremill/github-actions-workflows` auto-merge workflow
- Uses `SOFTWAREMILL_CI_PR_TOKEN` PAT to trigger downstream CI on merge
to main
- Dependabot PRs labeled `automerge` via `dependabot.yml` config
- Follows sttp-ai/tapir pattern

**Dependabot:**
- `gradle` ecosystem with two groups: `production` (exposed, spring,
jackson, drivers) and `testing` (kotest, testcontainers, wiremock) —
separate risk levels, auto-classified via `dependency-type`
- `github-actions` ecosystem for keeping workflow actions current

**Out of scope (deferred to KOJAK-35):**
- Release-drafter, release notes, Maven Central publishing

## Test plan
- [ ] CI workflow triggers on this PR with two matrix jobs (JDK 21, JDK
25)
- [ ] `ktlintCheck` passes on both JDK versions
- [ ] All tests pass on both JDK versions (including
Testcontainers-based integration tests)
- [ ] Create `automerge` label in GitHub repo settings (or verify
Dependabot auto-creates it on first PR)

Author: endrju19

.github/dependabot.yml

@@ -0,0 +1,24 @@
+version: 2
+updates:
+  # Keep Gradle dependencies up to date
+  - package-ecosystem: "gradle"
+    directory: "/"
+    labels:
+      - "automerge"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 10
+    groups:
+      production:
+        dependency-type: "production"
+      testing:
+        dependency-type: "development"
+
+  # Keep GitHub Actions up to date
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    labels:
+      - "automerge"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 10

.github/workflows/ci.yml

@@ -0,0 +1,51 @@
+name: CI
+on:
+  pull_request:
+    branches: [ main ]
+  push:
+    branches: [ main ]
+
+permissions:
+  contents: write       # auto-merge requirement
+  pull-requests: write  # auto-merge requirement
+
+jobs:
+  ci:
+    runs-on: ubuntu-24.04
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [ "21", "25" ]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up JDK ${{ matrix.java }}
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: ${{ matrix.java }}
+
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@748248ddd2a24f49513d8f472f81c3a07d4d50e1 # v4.4.4
+
+      - name: Check formatting
+        run: ./gradlew ktlintCheck
+
+      - name: Test
+        run: ./gradlew test
+
+      - name: Upload test results
+        uses: actions/upload-artifact@v4
+        if: success() || failure()
+        with:
+          name: test-results-java-${{ matrix.java }}
+          path: '**/build/test-results/test/TEST-*.xml'
+
+  auto-merge-dependabot:
+    # only for PRs by dependabot[bot]
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    needs: [ ci ]
+    uses: softwaremill/github-actions-workflows/.github/workflows/auto-merge.yml@main
+    secrets:
+      github-token: ${{ secrets.SOFTWAREMILL_CI_PR_TOKEN }}