Add runtime MCP server configuration management UI

[adamd9]

Summary

• replace the static MCP server JSON with a runtime-managed store that supports CRUD operations, legacy import, and a reloadable discovery pipeline
• expose the runtime MCP server data via new backend API routes, refresh the tool registry on reload, and make MCP tools re-registration idempotent
• add a dedicated /mcp-servers management page in the webapp (linked from the session configuration panel) for editing servers and trigger reloads, and update build scripts to skip copying the removed config directory

Testing

• npm run build
• npm run backend:build

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https://chatgpt.com/codex/tasks/task_e_68cf126fd8648328a5d95f19b6badfdb