docs: make the repository portable and installation-first

[chjoel0621]

Summary

• Reorganize the public repository around first-time plugin installation, with English as the default README and a prominent Korean README link.
• Add portable documentation navigation, repository path-leak detection, Markdown link validation, and CI enforcement.
• Remove workstation-specific assumptions from marketing tooling and make expected runtime failures fail-fast and leak-safe.
• Keep the plugin runtime, viewer, demos, and plugin version unchanged.

Verification

• npm run check:all passed on the final branch head.
• Repository audit tests: 26 passed, 0 failed.
• Path and documentation audits passed.
• Full unit, contract, packaging, installed-plugin, semantic evaluation, and browser regression suites passed.
• Independent final review found no open Critical or Important issues.

Scope boundary

This PR is Phase A only. It does not rewrite public Git history or force-push any branch. The separately documented Phase B history sanitization remains unexecuted and requires its own manifest review and explicit approval gate.