Unify bilingual introduction and user guides

[johnfkoo951]

Summary

• Standardize English/Korean README structure and link the unified product website.
• Add comprehensive bilingual user guides for installation, first use, commands, settings, privacy, limitations and troubleshooting.
• Keep runtime code, release versions, licensing and upstream attribution unchanged.

Verification

• Source and current release/community registry checked.
• Guide bodies match the reviewed vault masters and live website copies.
• Markdown fences, links and git diff whitespace checks passed.
• No live API calls, imports, migrations or plugin release performed by this documentation change.