Support key-value option lines

[AgentGoose32]

Fixes #72

Summary

• Allows options to be provided in the key/value line format shown in workflow YAML examples, e.g. keep_releases: 7.
• Keeps JSON object support for existing users.
• Fails the action with a clear message when the options input is neither JSON nor key/value lines, instead of silently ignoring invalid JSON.
• Rebuilds dist/index.js.

Validation

• npm run typecheck
• npm run build
• npm run format:check
• git diff --check