Chore: Typescript cleanup (1 / N) (#7817)

## Summary

Remove 178 `@ts-expect-error` suppressions (935 → 757, 19% reduction) by
fixing underlying type issues instead of suppressing errors.

## Changes

- **What**: Type safety improvements across `src/lib/litegraph/` and
related test files
  - Prefix unused callback parameters with `_` instead of suppressing
  - Use type intersections for mock methods on real objects
  - Use `Partial<T>` for incomplete test objects instead of `as unknown`
  - Add non-null assertions after `.toBeDefined()` checks in tests
  - Let TypeScript infer vitest fixture parameter types
- **Breaking**: None

## Review Focus

- `LGraphCanvas.ts` has the largest changes (232 lines) — all mechanical
unused parameter fixes
- Test files use type intersection pattern for mocks: `node as
LGraphNode & { mockFn: ... }`
- Removed dead code: `src/platform/cloud/onboarding/auth.ts` (47 lines,
unused)

### Key Files
| File | Change |
|------|--------|
| `LGraphCanvas.ts` | 57 suppressions removed (unused params) |
| `subgraph/__fixtures__/*` | Fixture type improvements |
| `*.test.ts` files | Mock typing with intersections |

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7817-WIP-Chore-Typescript-cleanup-2da6d73d365081d1ade9e09a6c5bf935)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>

src/platform/cloud/onboarding/auth.ts

@@ -127,53 +127,6 @@ export async function getSurveyCompletedStatus(): Promise<boolean> {
   }
 }
 
-// @ts-expect-error - Unused function kept for future use
-async function postSurveyStatus(): Promise<void> {
-  try {
-    const response = await api.fetchApi(`/settings/${ONBOARDING_SURVEY_KEY}`, {
-      method: 'POST',
-      headers: {
-        'Content-Type': 'application/json'
-      },
-      body: JSON.stringify({ [ONBOARDING_SURVEY_KEY]: undefined })
-    })
-
-    if (!response.ok) {
-      const error = new Error(
-        `Failed to post survey status: ${response.statusText}`
-      )
-      captureApiError(
-        error,
-        '/settings/{key}',
-        'http_error',
-        response.status,
-        'post_survey_status',
-        {
-          route_template: '/settings/{key}',
-          route_actual: `/settings/${ONBOARDING_SURVEY_KEY}`
-        }
-      )
-      throw error
-    }
-  } catch (error) {
-    // Only capture network errors (not HTTP errors we already captured)
-    if (!isHttpError(error, 'Failed to post survey status:')) {
-      captureApiError(
-        error as Error,
-        '/settings/{key}',
-        'network_error',
-        undefined,
-        'post_survey_status',
-        {
-          route_template: '/settings/{key}',
-          route_actual: `/settings/${ONBOARDING_SURVEY_KEY}`
-        }
-      )
-    }
-    throw error
-  }
-}
-
 export async function submitSurvey(
   survey: Record<string, unknown>
 ): Promise<void> {