Replace local PortalManifest type in spa bootstrap.ts with shared type

## Context

`packages/vite-plugins/spa/src/html/bootstrap.ts` defines a local `PortalManifest` type with a `// @todo - add type for portal manifest when available` comment, pending an official/shared type for the portal manifest shape once it's published elsewhere.

## Task

Replace the local `PortalManifest` type in `bootstrap.ts` with the shared/official type once one is published, removing the local duplicate.

_Filed while resolving `fusion-lint`'s `no-todo-without-issue` rule._

Read packages/vite-plugins/spa/src/html/bootstrap.ts and search the repository for the published shared portal manifest type. Confirm that the official type is available before replacing the local PortalManifest definition; done means the duplicate type and its todo comment are removed.

Written by the indexing model from the issue text.