feat: add React Router adapter

[farizanjum]

Summary

• add @dualmark/remix for React Router v7 Framework Mode
• generate markdown resource routes and /llms.txt from Dualmark config
• add entry-server negotiation for bot user agents and Accept: text/markdown
• add examples/remix-blog plus docs and release metadata

Testing

• bun run --filter @dualmark/remix test
• bun run --filter @dualmark/remix typecheck
• bun run --filter @dualmark/remix build
• bun run --filter dualmark-example-remix-blog build
• bun run --filter dualmark-docs build
• node packages/cli/dist/cli.js verify http://localhost:5174/posts/hello returned 125/125 under react-router dev
• node packages/cli/dist/cli.js verify http://localhost:3000/posts/hello returned 125/125 under react-router-serve

Notes

• slugStrategy: "catch-all" is intentionally rejected for now because React Router splats cannot safely express nested *.md routes without catching human HTML paths.
• The current React Router docs entry point is https://reactrouter.com/start/framework/installation.

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