fix(ui): drop unused runtimeFetch import in gitApi

d353638f3 replaced both `runtimeFetch('/api/small-model/generate')` calls
with `requestSmallModel` but left the original import in place, so
`@typescript-eslint/no-unused-vars` fails `bun run --filter '*' lint` on
main:

  packages/ui/src/lib/gitApi.ts
    5:10  error  'runtimeFetch' is defined but never used

This blocks CI for every open PR, since pull_request runs lint against the
merge with main.

packages/ui/src/lib/gitApi.ts

@@ -2,7 +2,6 @@
 import * as gitHttp from './gitApiHttp';
 import { opencodeClient } from './opencode/client';
 import { renderMagicPrompt } from './magicPrompts';
-import { runtimeFetch } from './runtime-fetch';
 import { requestSmallModel } from './smallModelRequest';
 import { materializeOpenDraftSession, useSessionUIStore } from '@/sync/session-ui-store';
 import { useSelectionStore } from '@/sync/selection-store';