The `client/` workspace was never type-checked: the existing typecheck
job only covered `packages/` and `api/`, and Vite/esbuild transpiles
without type-checking, so type errors shipped through every CI gate.
- Add a `typecheck` job to frontend-review.yml running `tsc --noEmit`
over `client/` (zero tolerance), reusing the data-provider +
client-package build artifacts. Triggers on `client/**`,
`packages/client/**`, `packages/data-provider/**`.
- Fix all 168 pre-existing client type errors this surfaced (source +
tests), including genuine latent bugs:
- `getFileConfig()` was typed as merged `FileConfig`, but the server
returns the raw config that `mergeFileConfig()` consumes (`TFileConfig`).
- SidePanel/Agents `Retrieval`/`ImageVision` were bound to `AgentForm`
but use the assistants `Capabilities` enum → `AssistantForm`.
- `useSearchResultsByTurn` read a `sources` field its type lacked.
- Removed orphaned dead code: `Artifacts/Mermaid.tsx` (imported a
never-installed dep) and dead barrel re-exports (`./Plugins`, `./MCPAuth`).
- Narrow `client/tsconfig.json` to the client app (drop `../e2e` and
`../config/translations`, which reference backend/tooling modules) so
the gate's scope matches its trigger.
No `any`/`@ts-ignore`/`as unknown as`. Localized newly-surfaced strings.
