Reorganize README: extract skill/agent docs into docs/skills.md and docs/agents.md

[kluzny]

Summary

The README currently contains both a table-of-contents and full narrative descriptions for every skill and agent. As the repo grows, this will get unwieldy. Split it so the README is a concise TOC and the detail lives in dedicated docs files.

Proposed changes

Create docs/skills.md

• Move the per-skill sections (prerequisites, what it covers, reference links) out of the README into this file
• One ## section per skill

Create docs/agents.md

• Move the sub-agents section detail out of the README into this file
• One ## section per agent

Slim down README.md

• Keep the Installation section as-is
• Replace the Skills detail with the summary table + a link to docs/skills.md for full descriptions
• Replace the Sub-Agents detail with the summary table + a link to docs/agents.md for full descriptions

Goal

README becomes a quick-reference table of contents. Readers who want full details follow links to the dedicated docs files or directly to the skill directories.