ci: add comprehensive quality checks before Docker build

Added test job that must pass before building Docker image:
- Code formatting check (mix format --check-formatted)
- Compilation with warnings as errors
- Credo static analysis (--strict mode)
- Full test suite with PostgreSQL + TimescaleDB

Build job now depends on test job passing (needs: test).

This prevents broken code from being deployed to production.

.forgejo/workflows/build.yaml

@@ -14,8 +14,70 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  test:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: timescale/timescaledb:latest-pg17
+        env:
+          POSTGRES_USER: postgres
+          POSTGRES_PASSWORD: postgres
+          POSTGRES_DB: towerops_test
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+        ports:
+          - 5432:5432
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Elixir
+        uses: erlef/setup-beam@v1
+        with:
+          otp-version: '27.1'
+          elixir-version: '1.17.3'
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libsnmp-dev snmp-mibs-downloader
+
+      - name: Restore dependencies cache
+        uses: actions/cache@v4
+        with:
+          path: |
+            deps
+            _build
+          key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }}
+          restore-keys: ${{ runner.os }}-mix-
+
+      - name: Install dependencies
+        run: mix deps.get
+
+      - name: Check code formatting
+        run: mix format --check-formatted
+
+      - name: Compile with warnings as errors
+        run: mix compile --warnings-as-errors
+        env:
+          MIX_ENV: test
+
+      - name: Run Credo
+        run: mix credo --strict
+
+      - name: Run tests
+        run: mix test --warnings-as-errors
+        env:
+          MIX_ENV: test
+          DATABASE_URL: postgresql://postgres:postgres@localhost:5432/towerops_test
+
   build:
     runs-on: ubuntu-latest
+    needs: test
     steps:
       - name: Checkout code
         uses: actions/checkout@v4