ci: enforce coverage thresholds in CI pipeline

- Run frontend tests with coverage thresholds (15% lines/statements)
- Add llvm-tools-preview component for Rust coverage
- Install cargo-llvm-cov and enforce 50% line coverage for backend
- CI will now fail if coverage drops below thresholds

.gitea/workflows/ci.yml

@@ -49,13 +49,13 @@ jobs:
       - name: Run Svelte Check
         run: pnpm check
 
-      - name: Run frontend tests
+      - name: Run frontend tests with coverage
-        run: pnpm test
+        run: pnpm test:coverage
 
       - name: Setup Rust
         uses: dtolnay/rust-toolchain@stable
         with:
-          components: clippy
+          components: clippy, llvm-tools-preview
 
       - name: Cache Rust dependencies
         uses: actions/cache@v4
@@ -68,13 +68,16 @@ jobs:
             src-tauri/target/
           key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
 
+      - name: Install cargo-llvm-cov
+        run: cargo install cargo-llvm-cov --locked
+
       - name: Run Clippy
         working-directory: src-tauri
         run: cargo clippy --all-targets --all-features -- -D warnings
 
-      - name: Run Rust tests
+      - name: Run Rust tests with coverage
         working-directory: src-tauri
-        run: cargo test
+        run: cargo llvm-cov --fail-under-lines 50
 
   build-linux:
     name: Build Linux