Gemspec hardening: require MFA for pushes, add metadata URIs

[kanejamison]

Problem

bunko.gemspec is missing supply-chain hardening metadata before the public RubyGems release.

Proposed solution

spec.metadata["rubygems_mfa_required"] = "true"
spec.metadata["source_code_uri"] = spec.homepage
spec.metadata["bug_tracker_uri"] = "#{spec.homepage}/issues"

Acceptance criteria

• Pushing the gem requires MFA on rubygems.org.
• Metadata URIs visible on the gem's rubygems page.

[kanejamison]

This was implemented in PR #79 (commit bcee6cc), which is now on main. The gemspec sets:

spec.metadata["rubygems_mfa_required"] = "true"
spec.metadata["source_code_uri"] = spec.homepage
spec.metadata["bug_tracker_uri"] = "#{spec.homepage}/issues"

plus homepage_uri and changelog_uri. Closing as completed.

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