fix: resolve ruff lint errors and add lint CI job

Remove unused imports (deque, sys, Opcode, struct, _REPLAY_ADJUSTABLE_OPCODES)
across 4 active Python files and refactor semicolons to separate statements
in radar_protocol.py. Add ruff lint job to CI workflow targeting only the
active files (excludes legacy GUI_V*.py and v7/).

.github/workflows/ci-tests.yml

@@ -7,6 +7,34 @@ on:
     branches: [main, develop]
 
 jobs:
+  # ===========================================================================
+  # Job 0: Ruff Lint (active Python files only)
+  # Excludes legacy GUI_V*.py files and untracked v7/ directory
+  # ===========================================================================
+  lint:
+    name: Ruff Lint (active files)
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Python 3.12
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install ruff
+        run: pip install ruff
+
+      - name: Run ruff on active files
+        run: |
+          ruff check \
+            9_Firmware/9_3_GUI/radar_protocol.py \
+            9_Firmware/9_3_GUI/radar_dashboard.py \
+            9_Firmware/9_3_GUI/smoke_test.py \
+            9_Firmware/9_3_GUI/test_radar_dashboard.py
+
   # ===========================================================================
   # Job 1: Python Host Software Tests (58 tests)
   # radar_protocol, radar_dashboard, FT2232H connection, replay, opcodes, e2e