docs: simplify README and harness docs

[eunaverse]

Summary

• simplify the active docs path so README plus architecture are the maintained sources for current work
• tighten README setup guidance for Claude Desktop, Docker, GitHub repo specs, and Obsidian vault usage
• add a real Claude Desktop screenshot example and keep older core-understanding links working through a deprecated compatibility stub

Validation

• rg --files AGENTS.md README.md docs .agents/docs .agents/skills
• git diff --check
• git diff --cached --check
• repeated five-reviewer subagent review passes during the docs rewrite loop

Notes

• 관련 이슈 없음