chore: fix build and lint errors and add CI checks

Author: Bot

.github/workflows/ci.yml

@@ -0,0 +1,49 @@
+name: CI
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+    branches: [ main, master ]
+
+jobs:
+  backend-build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./backend
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
+      with:
+        node-version: '20'
+    - run: npm install
+    - run: npm run build
+
+  frontend-build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./frontend
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
+      with:
+        node-version: '20'
+    - run: npm install
+    - run: npm run build
+
+  contracts-build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./contracts
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Rust toolchain
+      uses: dtolnay/rust-toolchain@stable
+      with:
+        components: clippy, rustfmt
+    - run: cargo fmt --check
+    - run: cargo clippy -- -D warnings
+    - run: cargo build