docs(readme-guide): add DeepWiki badge to standard set

[bborbe]

Summary

• Add DeepWiki as a fourth standard badge in CLI tool + Go library templates
• Expand the Badges section with one-line rationale per badge (what it signals, why include it)

Test plan

• Visual check rendered guide reads well

[ben-s-pull-request-reviewer]

Reviewed by ben-s-pull-request-reviewer[bot] — no concerns flagged.