[codex] add MCP external-agent mode

[Flowershangfromthebranches]

Summary

• add a new @actalk/inkos-mcp workspace package with stdio MCP server and inkos-mcp bin
• expose MCP tools/resources/prompts for project status, book inspection, deterministic import, context bundling, write-back, export, diagnosis, and index repair
• add agent-mediated create/import/continue workflows so Codex/Claude Code handle LLM generation and settlement while InkOS manages project files
• document MCP mode and clarify that default MCP flows do not require InkOS LLM API keys or read secrets

Test plan

• pnpm build
• pnpm test
• pnpm typecheck
• pnpm verify:publish-manifests
• node -e "import('./packages/mcp/dist/index.js').then(() => console.log('import-ok'))"

Breaking changes

None. Existing Studio, CLI, TUI, and OpenClaw interaction paths remain unchanged.