Add GoReleaser and pre-built binary distribution

[ChrisJBurns]

Summary

This PR improves action performance by using pre-built binaries instead of compiling Go code on every run.

Changes

File	Description
.goreleaser.yml	GoReleaser config for multi-platform binary builds (linux/darwin × amd64/arm64)
.github/workflows/release.yml	Workflow that triggers on v* tags to build and publish releases
action.yml	Updated to download pre-built binaries instead of go run
.gitignore	Added dist/ directory

Performance Improvement

Metric	Before	After
Startup time	~30 seconds	~2 seconds
Method	Compile on every run	Download pre-built binary

How It Works

1. When you push a tag like v1.2.0, the release workflow runs
2. GoReleaser builds binaries for all platforms and creates a GitHub release
3. When users reference @v1.2.0, the action downloads the matching binary

Version Validation

The action now validates that it's referenced with a proper version tag:

# ✅ Valid
uses: stacklok/releaseo@v1.2.0

# ❌ Invalid - will error
uses: stacklok/releaseo@main
uses: stacklok/releaseo@some-branch

Error messages guide users to the correct usage:

::error::Invalid version 'main'. Please use a semantic version tag (e.g., @v1.0.0). Using @main or @branch-name is not supported.

Breaking Change

⚠️ Users must reference this action with a version tag (e.g., @v1.0.0)

Using @main or branch names is no longer supported. This ensures reproducible builds and better security.

Test plan

• GoReleaser config syntax is valid
• Build and tests pass
• Create a test release tag to verify the full flow (post-merge)

🤖 Generated with Claude Code