ci: add GitHub Actions workflow and devcontainer config

- CI runs go vet, go test -race, and go build against Go 1.25 and 1.26
- Devcontainer uses Go 1.25 image with Node.js for conformance test generation

Co-authored-by: Ona <no-reply@ona.com>

Author: csweichel

.devcontainer/devcontainer.json

@@ -0,0 +1,7 @@
+{
+	"name": "xterm-go",
+	"image": "mcr.microsoft.com/devcontainers/go:1.25",
+	"features": {
+		"ghcr.io/devcontainers/features/node:1": {}
+	}
+}

.github/workflows/ci.yaml

@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: ["1.25", "1.26"]
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go-version }}
+
+      - name: Vet
+        run: go vet ./...
+
+      - name: Test
+        run: go test -race -count=1 ./...
+
+      - name: Build
+        run: go build ./...