docs(mcp-server): sync README with canonical MCP docs

[kvz]

What

• rewrite packages/mcp-server/README.md to align with website MCP docs
• keep self-hosted as default happy path and hosted endpoint as fallback
• document auth model, tool surface, limits, URL/template behavior, metrics, and docs links
• add inline ## Contributing with package-relevant setup and validation commands
• update server card documentationUrl to https://transloadit.com/docs/sdks/mcp-server/

Why

Keep product docs and package docs in sync, with one clear canonical MCP docs owner page.

Validation

• corepack yarn check

Related

• content docs PR: https://github.com/transloadit/content/pull/4834

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Run HTTP quickstart via npx to avoid missing binary

The new self-hosted HTTP quickstart command invokes transloadit-mcp directly, but this README’s install step uses npm install @transloadit/mcp-server (local install), which does not put that binary on the user’s shell PATH. In that common setup, the quickstart fails with command not found unless users happened to install globally; use npx -y @transloadit/mcp-server http ... (or explicitly document global install) so the documented happy path works.

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