fix: align agent-platform guide with skills (.agents/skills, /skill invocations)

[GumpZH]

Summary

The agent-platform/* guide targets the newer agent-platform-railway template, where the five lifecycle prompts ship as Claude Code skills under .agents/skills/<name>/SKILL.md (invoked as /create-new-agent, /improve-agent, /extend-agent, /eval-and-improve, /review-and-improve). There is no docs/ folder in that repo.

Several pages still referenced the old docs/<name>.md prompt paths, so following them literally (e.g. Run docs/create-new-agent.md) fails. This PR updates all of them to the skill invocations the template actually documents in its README/AGENTS.md.

Pages fixed (agent-platform/*)

• run-local.mdx — Summary bullet: docs/ folder → .agents/skills/ folder of skills.
• create-agent.mdx — prose + code block → /create-new-agent; "five prompts" → "five skills".
• improve-agent.mdx — two bullets + two code blocks → /improve-agent, /extend-agent; "two prompts" → "two skills".
• evals.mdx — prose + code block → /improve-agent, /eval-and-improve.
• next-steps.mdx — code block → /review-and-improve; "prompt" → "skill".

Deliberately NOT changed

The tutorials/agent-platform/* pages clone the older agentos-railway-template, which really does ship a docs/*.md folder. Their docs/...md references are correct for that repo and were left untouched.

🤖 Generated with Claude Code