feat(backend): test suite (#15)

* ci: add backend tests workflow

* test: add comprehensive backend integration and unit tests

* fix: use REAL literals in COALESCE for SQLite type compatibility

Author: cachebag

.github/workflows/tests.yml

@@ -0,0 +1,42 @@
+name: Tests
+
+on:
+  pull_request:
+    branches: [master]
+  push:
+    branches: [master]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  backend-tests:
+    name: Backend Tests
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache cargo registry
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            backend/target
+          key: ${{ runner.os }}-cargo-test-${{ hashFiles('backend/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-test-
+            ${{ runner.os }}-cargo-
+
+      - name: Run tests
+        run: cargo test --all-features --verbose
+
+      - name: Run tests with release optimizations
+        run: cargo test --release --all-features