Refactor metadata fetch and reorganize docs/workflows

[spiegel-im-spiegel]

Summary

• Replace web metadata fetching in makelink.New with github.com/goark/webinfo
• Reorganize GitHub Actions workflows to ci + CodeQL and keep release build
• Add .github/copilot-instructions.md and update README.md
• Improve exported GoDoc comments across packages
• Improve history handling:
  • ignore os.ErrNotExist on initial history load
  • save with O_TRUNC while preserving explicit 0600 permission
  • append history only on successful link generation
• Refresh generated dependency.png

Validation

• task test
• task govulncheck
• task (default)

Notes

• Release process docs now match the tag-triggered build workflow behavior.

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