feat: clarify local RAG workflows and package guides

[jb-thery]

Summary

• clarify the landing workflows so each step explains the source, Ragmir retrieval, and cited result
• align the Feature Map layout and package positioning around local RAG for coding agents
• rewrite the npm package READMEs with agent and script workflows before TypeScript APIs
• keep English and French copy aligned and remove nonessential command footers from workflow cards

Validation

• pnpm validate
• pnpm lint
• pnpm --filter @jcode.labs/ragmir-landing check
• pnpm --filter @jcode.labs/ragmir-landing build
• pnpm package:check
• browser checks in English and French at desktop and mobile widths
• GitNexus change detection: low risk, no affected execution flow