ci(a11y): add djlint HTML accessibility lint to CI pipeline

- Add html-lint job to CI that runs djlint on all PRs
- Configure djlint in pyproject.toml with Jinja2 profile and accessibility rules
- Add djlint to requirements-dev.txt
- Expand accessibility section in frontend Copilot instructions (WCAG 2.1 AA)
- Wire html-lint into CI dependency chain (test/mypy/build depend on it)

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

.github/workflows/ci.yml

@@ -61,6 +61,28 @@ jobs:
         # ruff format only supports --check; do not pass --fix here
         run: ruff format --check app/ tests/
 
+  # ══════════════════════════════════════════════════════════════════════════
+  # Stage 1b: HTML Accessibility Lint (catches a11y regressions early)
+  # ══════════════════════════════════════════════════════════════════════════
+
+  html-lint:
+    name: HTML Accessibility Lint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install djLint
+        run: pip install djlint>=1.36.0
+
+      - name: Lint HTML templates for accessibility
+        run: djlint frontend/templates/ --lint
+
   # ══════════════════════════════════════════════════════════════════════════
   # Stage 2a: Dependency Vulnerability Scan (runs in parallel with lint)
   # ══════════════════════════════════════════════════════════════════════════
@@ -93,7 +115,7 @@ jobs:
   test:
     name: Tests
     runs-on: ubuntu-latest
-    needs: [lint, dependency-scan]  # Wait for lint and dependency scan before running tests
+    needs: [lint, html-lint, dependency-scan]  # Wait for lint, HTML a11y lint, and dependency scan before running tests
     services:
       redis:
         image: redis:7
@@ -160,7 +182,7 @@ jobs:
   mypy:
     name: Mypy
     runs-on: ubuntu-latest
-    needs: [lint, dependency-scan]  # Wait for lint and dependency scan before running type checks
+    needs: [lint, html-lint, dependency-scan]  # Wait for lint, HTML a11y lint, and dependency scan before running type checks
     steps:
       - name: Checkout Code
         uses: actions/checkout@v4
@@ -185,7 +207,7 @@ jobs:
   build:
     name: Build & Push Docker Image
     runs-on: ubuntu-latest
-    needs: [test, lint, mypy, dependency-scan]
+    needs: [test, lint, html-lint, mypy, dependency-scan]
     if: github.event_name == 'push'
 
     steps: