[codex] Remove OAuth and MCP support

[hhhjin]

Summary

• remove the Better Auth OAuth provider and all MCP server routes, handlers, and supporting client pages
• drop the OAuth/JWKS tables from the auth schema and add a migration that removes them from existing databases
• remove the OAuth/MCP-specific tests and docs references that no longer apply

Why

This change removes the OAuth-backed MCP integration surface from mdto so the codebase, schema, and documentation match the currently supported product surface.

Impact

The app continues to support the existing Better Auth sign-in flow and API key functionality, but no longer exposes OAuth2, JWKS, or MCP endpoints.

Validation

• pnpm lint:fix
• pnpm test
• pnpm build (client/server builds completed, but prerender failed to start the Vite preview server in the local environment)

[gemini-code-assist]

Code Review

This pull request removes the Model Context Protocol (MCP) server integration and its associated OAuth provider functionality, including UI routes, database schemas, and related dependencies. The review suggests improving the authentication configuration to support dynamic origins for local development and ensuring the migration script is idempotent by using DROP TABLE IF EXISTS statements.