feat: add Gitea CI workflow with podman-based lint and link check

- Markdown lint via markdownlint-cli2 container
- Internal cross-reference checker for See Also sections
- Both jobs run on linux runner using podman containers

.gitea/workflows/ci.yml

@@ -0,0 +1,35 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  lint:
+    runs-on: linux
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Markdown lint
+        run: |
+          podman run --rm \
+            -v "${{ github.workspace }}:/work:Z" \
+            docker.io/davidanson/markdownlint-cli2:v0.17.2 \
+            "**/*.md"
+
+  link-check:
+    runs-on: linux
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Check internal links
+        run: |
+          podman run --rm \
+            -v "${{ github.workspace }}:/work:Z" \
+            -w /work \
+            docker.io/library/python:3.12-slim \
+            python3 scripts/check-links.py