fix(mcp): preserve nested schema references in tool signatures

[aryasaatvik]

Account-routed imported tools currently advertise unknown for referenced input fields and responses because their JSON Schema references point into account branches. Project those local references into distinct root definitions before rendering signatures, preserving each account's types and recursive references.

// Before
{ path: { app_id: unknown; account_id: unknown } }
// After
{ path: { app_id: string; account_id: string } }

The projection changes only the schemas passed to CodeMode; original tool schemas and validation remain intact. Existing account-routing coverage now requires distinct account literals, escaped definition names, recursive sibling fields, and a typed output consumer.

Four focused self-host scenarios pass. The regression fails against the original renderer at the expected value: "work" assertion. Full bun run check remains blocked by twelve existing implicit-any errors in the desktop E2E support and release scenario; core typechecking, formatting, linting, dependency patches, and the remaining contract checks pass.

template-accounts.spec.ts
mcp-catalog.spec.ts
mcp-search-concise.spec.ts
framework-discovery.spec.ts
framework-authoring.spec.ts