feat(openclaw): update worker workspace markdown templates

[jialudev]

Summary

• Replace the OpenClaw worker workspace bootstrap file from AGENT.md to AGENTS.md and split runtime guidance into AGENTS, IDENTITY, TOOLS, and HEARTBEAT markdown files.
• Stop seeding placeholder memory markdown for OpenClaw workers; OpenClaw supports root MEMORY.md when users create it, but default workspace memory is expected to live under memory/*.md or be managed by memory tools.
• Update OpenClaw skill installer docs and scripts to install/list skills from OPENCLAW_WORKSPACE, defaulting to ~/.openclaw/workspace, instead of Codex/PicoClaw paths.
• Add template embedding and workspace seeding tests for the new OpenClaw bootstrap layout and deprecated-file removal.

Verification

• env GOCACHE=/Users/jared/opencsg-workspace/csgship/csgclaw/.gocache go test ./internal/agent