feat: Add GoReleaser workflow for cross-platform binary releases

- Add .goreleaser.yml for automated releases
- Add .github/workflows/release.yml triggered on version tags
- Build matrix: darwin/linux/windows for amd64/arm64
- Update install.sh to download from GitHub releases first
- Add install.sh symlink at root for convenience
- Update RELEASING.md with automation documentation

Closes #89 (vendorable executables as releases)
Implements bd-85

Amp-Thread-ID: https://ampcode.com/threads/T-02baad43-7e97-4710-bc60-777643d2eb77
Co-authored-by: Amp <amp@ampcode.com>

.github/workflows/release.yml

@@ -0,0 +1,32 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+permissions:
+  contents: write
+
+jobs:
+  goreleaser:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.24'
+
+      - name: Run GoReleaser
+        uses: goreleaser/goreleaser-action@v6
+        with:
+          distribution: goreleaser
+          version: '~> v2'
+          args: release --clean
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}