feat(phase-34): resolve blocking tech debt — Redis, domain exceptions, indexes, CI

Foundational changes required before any new feature work can begin.

- 0.1 Redis infrastructure: add redis:7-alpine to docker-compose dev and prod,
  REDIS_URL config, singleton client in app/infrastructure/redis_client.py
- 0.2 Token blacklist on Redis SEC-001: replace in-memory dict with Redis SETEX
  keyed by jti, auto-expiring TTL derived from token exp
- 0.3 Database indexes SR-006: Alembic migration b019 with 5 composite indexes
  for scoring, MTTD/MTTR, remediation, and notification queries
- 0.4 Domain exceptions TD-003: app/domain/exceptions.py with typed errors,
  error_handler middleware mapping them to HTTP, services decoupled from FastAPI
- 0.5 Fix silenced exceptions TD-007: replace 4 bare except-pass blocks in
  test_workflow_service with logger.warning with exc_info
- 0.6 CI pipeline TD-009: GitHub Actions workflow with Postgres and Redis
  service containers, ruff lint, pytest; ruff.toml for baseline config

.github/workflows/ci.yml

@@ -0,0 +1,64 @@
+name: Aegis CI
+
+on:
+  push:
+    branches: [main, develop]
+  pull_request:
+    branches: [main]
+
+jobs:
+  lint-and-test:
+    runs-on: ubuntu-latest
+
+    services:
+      postgres:
+        image: postgres:15-alpine
+        env:
+          POSTGRES_DB: testdb
+          POSTGRES_USER: test
+          POSTGRES_PASSWORD: test
+        ports:
+          - 5432:5432
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+      redis:
+        image: redis:7-alpine
+        ports:
+          - 6379:6379
+        options: >-
+          --health-cmd "redis-cli ping"
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+
+    defaults:
+      run:
+        working-directory: backend
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+          cache: pip
+          cache-dependency-path: backend/requirements.txt
+
+      - name: Install dependencies
+        run: |
+          pip install --upgrade pip
+          pip install -r requirements.txt
+          pip install ruff
+
+      - name: Lint
+        run: ruff check app/
+
+      - name: Test
+        env:
+          DATABASE_URL: postgresql://test:test@localhost:5432/testdb
+          REDIS_URL: redis://localhost:6379/0
+          SECRET_KEY: ci-test-secret-key-not-for-production
+        run: pytest tests/ -v --tb=short