fix: standardize SwiftLint workflow with proper container and caching

Replaced minimal SwiftLint workflow with proper implementation that:
- Uses Swift 6.2 container for consistency
- Builds SwiftLint from source (not relying on preinstalled version)
- Implements caching for faster runs (~30s vs 11m)
- Runs on both push and PR (not just PR)
- Uses --strict flag (fails on warnings)
- Removes continue-on-error (failures should block merges)
- Adds concurrency group to cancel outdated runs

Matches swift-html-to-pdf configuration.

Author: coenttb

.github/workflows/swiftlint.yml

@@ -1,13 +1,48 @@
 name: SwiftLint
+
 on:
+  push:
+    branches:
+      - main
   pull_request:
-    branches: [main]
+    branches:
+      - main
+
+concurrency:
+  group: swiftlint-${{ github.ref }}
+  cancel-in-progress: true
 
 jobs:
   lint:
+    name: SwiftLint
     runs-on: ubuntu-latest
+    container: swift:6.2
     steps:
       - uses: actions/checkout@v5
-      - name: SwiftLint
-        run: swiftlint lint
-        continue-on-error: true
+
+      - name: Restore swiftlint cache
+        id: cache-swiftlint-restore
+        uses: actions/cache/restore@v4
+        with:
+          path: /usr/local/bin/swiftlint
+          key: ${{ runner.os }}-swiftlint-v1
+
+      - name: Install swiftlint
+        if: steps.cache-swiftlint-restore.outputs.cache-hit != 'true'
+        run: |
+          git clone --depth 1 --branch main https://github.com/realm/SwiftLint.git
+          cd SwiftLint
+          swift build -c release
+          cp .build/release/swiftlint /usr/local/bin/
+          cd ..
+          rm -rf SwiftLint
+
+      - name: Lint
+        run: swiftlint lint --strict --reporter github-actions-logging
+
+      - name: Save swiftlint cache
+        uses: actions/cache/save@v4
+        if: steps.cache-swiftlint-restore.outputs.cache-hit != 'true'
+        with:
+          path: /usr/local/bin/swiftlint
+          key: ${{ runner.os }}-swiftlint-v1