Publish GitHub Releases with changes between tags

[eric642]

What

Adds a release workflow so that publishing a version on GitHub shows the changes between the two versions.

• .github/workflows/release.yml — triggers on pushing a v* tag (matches the existing git tag vX.Y.Z && git push --tags flow). It re-runs go vet ./... and go test -race ./... against the tagged commit as a pre-publish gate, then creates a GitHub Release via gh release create --verify-tag.
• scripts/release-notes.sh — generates the release body: every non-merge commit since the previous v* tag (- subject (shortSHA), auto-linkified by GitHub) plus a compare/<prev>...<new> link. Locally runnable to preview a release before tagging: bash scripts/release-notes.sh vX.Y.Z.
• CHANGELOG.md — documents that pushing a tag now auto-publishes the release, and how to preview notes locally.

Example release body

## What's Changed

- Accept 200 responses when connecting sandboxes (697a2c3)
- Move CI lint to golangci-lint v2 built from source (67df31c)

**Full Changelog**: https://github.com/eric642/e2b-go-sdk/compare/v0.1.1...v0.2.0

Notes

• The script handles the first-release case (no previous tag → list full history + a commits/<tag> link), the no-changes case, and a missing-tag error.
• fetch-depth: 0 is set so the workflow has full history/tags to diff against.
• Since these are new files, release.yml must land on main first; tags pushed afterward will trigger it.

Verification

• bash -n syntax check + valid YAML parse.
• Ran scripts/release-notes.sh against the existing v0.1.0 and v0.1.1 tags — correct diff ranges, compare links, and git@-remote → owner/repo parsing.

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