add CI workflow running go vet and go test

Adds .gitea/workflows/ci.yml: on push to main and on pull requests, run
`go vet ./...` then `go test ./...` in a golang:1.25-alpine container.

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

.gitea/workflows/ci.yml

@@ -0,0 +1,26 @@
+# Vet and test the package. This is a pure Go library -- no build
+# step, no services -- so CI just runs `go vet` then `go test` on
+# every push to main and every pull request.
+
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    container:
+      image: golang:1.25-alpine
+    steps:
+      - name: Install checkout dependencies
+        run: apk add --no-cache git nodejs
+      - uses: actions/checkout@v4
+      - name: go vet
+        run: go vet ./...
+      - name: go test
+        run: go test ./...