Add CI/CD pipeline: Gitea Actions (test + lint + deploy)

CI (every push):
- pytest with coverage (>=50% gate)
- ruff lint check
- mypy type check (non-blocking)

CD (main branch only, after CI passes):
- SSH deploy to production server
- git pull + pip install + supervisorctl restart

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/pre-commit.yml

@@ -0,0 +1,17 @@
+name: Nexus Pre-commit Checks
+
+on:
+  push:
+    branches: ["*"]
+
+jobs:
+  quick-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - run: pip install ruff
+      - name: Quick lint
+        run: ruff check server/ --select=E,F,W --diff