Epic: MCP Management Experience

## Description

Right now the **MCP setup flow** has rough edges — error states show the wrong UI (setup wizard instead of permission errors), embedded forms display duplicate titles and buttons that bypass wizard validation, and test coverage has gaps that let MCP action regressions slip through. Users get confusing experiences, and contributors can't trust the tests.

This epic polishes the MCP management flow — proper error/RBAC handling in the overview, clean embedded forms in the wizard, reliable e2e tests that don't select non-existent gateways, and complete suite-router mappings so MCP changes always trigger their tests. The setup flow becomes trustworthy instead of fragile.

Start with the MCP setup flow, especially the overview and embedded wizard forms, then review the existing e2e tests and suite-router mappings. Done means permission errors show the correct UI, embedded forms avoid duplicate titles and bypassed validation, e2e tests use available gateways, and MCP changes trigger their tests.

Written by the indexing model from the issue text.