Migrate CI from GitLab to Gitea Actions

Replace .gitlab-ci.yml with .gitea/workflows/ci.yml, keeping the same
lint/format/typecheck/pip-audit/pytest jobs against python:3.11-slim,
and update docs that referenced the old GitLab pipeline file.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -0,0 +1,77 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  lint:
+    name: lint:ruff
+    runs-on: ubuntu-latest
+    container: python:3.11-slim
+    steps:
+      - uses: actions/checkout@v4
+      - name: Cache pip
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pip
+          key: pip-${{ hashFiles('pyproject.toml') }}
+      - run: pip install -e ".[dev,plotting]"
+      - run: ruff check gallery plotstyle tests
+
+  format:
+    name: format:ruff
+    runs-on: ubuntu-latest
+    container: python:3.11-slim
+    steps:
+      - uses: actions/checkout@v4
+      - name: Cache pip
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pip
+          key: pip-${{ hashFiles('pyproject.toml') }}
+      - run: pip install -e ".[dev,plotting]"
+      - run: ruff format --check gallery plotstyle tests
+
+  typecheck:
+    name: typecheck:ty
+    runs-on: ubuntu-latest
+    container: python:3.11-slim
+    steps:
+      - uses: actions/checkout@v4
+      - name: Cache pip
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pip
+          key: pip-${{ hashFiles('pyproject.toml') }}
+      - run: pip install -e ".[dev,plotting]"
+      - run: ty check gallery plotstyle
+
+  vulnerabilities:
+    name: vulnerabilities:pip-audit
+    runs-on: ubuntu-latest
+    container: python:3.11-slim
+    steps:
+      - uses: actions/checkout@v4
+      - name: Cache pip
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pip
+          key: pip-${{ hashFiles('pyproject.toml') }}
+      - run: pip install -e ".[dev,plotting]"
+      - run: pip-audit
+
+  test:
+    name: test:pytest
+    runs-on: ubuntu-latest
+    container: python:3.11-slim
+    needs: [lint, format, typecheck, vulnerabilities]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Cache pip
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pip
+          key: pip-${{ hashFiles('pyproject.toml') }}
+      - run: pip install -e ".[dev,plotting]"
+      - run: python -m pytest tests/ -v