Add install script, CI workflows, and release pipeline

- Install script: curl-pipe-sh installer that downloads the right
  binary for the user's OS/arch from GitHub Releases
- CI workflow: runs go vet + go test for both Go modules and builds
  the web app on push/PR
- Release workflow: goreleaser builds cross-platform binaries
  (linux/darwin, amd64/arm64) on version tags
- Node-agent defaults BETTERNAS_CONTROL_PLANE_URL to
  https://api.betternas.com so users only need username/password

.github/workflows/release.yaml

@@ -0,0 +1,27 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*"
+
+permissions:
+  contents: write
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: apps/node-agent/go.mod
+          cache-dependency-path: apps/node-agent/go.sum
+      - uses: goreleaser/goreleaser-action@v6
+        with:
+          version: latest
+          args: release --clean
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}