feat: add bundled providers for official MCP servers

[manojbajaj95]

Summary

Add bundled OAuth/API-key provider configs for the official MCP (Model Context Protocol) servers maintained by Anthropic and listed in the official MCP registry.

Motivation

Authsome already ships bundled providers for GitHub, Google, Okta, Linear, and OpenAI. Many MCP-native tools require OAuth connections to official MCP servers. Bundling these configs lowers friction for users who want to connect to officially-supported MCP services.

Scope

Only official MCP servers — servers listed at the official MCP registry (modelcontextprotocol.io) or maintained in the modelcontextprotocol/servers repository. Community/third-party servers are explicitly out of scope for this issue.

Work Items

• Audit the official MCP server list and identify which servers expose OAuth or API-key flows
• Add a bundled JSON provider config for each qualifying server under src/authsome/auth/bundled_providers/
• (Optional) Add a scripts/sync_mcp_providers.py script that fetches the official server list and regenerates the configs, so the list can be kept up-to-date with upstream changes
• Update README.md / provider docs to list newly added MCP providers
• Add tests covering at least one new provider config

References

• Official MCP servers repo: https://github.com/modelcontextprotocol/servers
• MCP spec: https://modelcontextprotocol.io