Fix fetch credentials option casing

[tristanmanchester]

Summary

• Change the affected fetch request option objects from the ignored Credentials property to the standard lowercase credentials property.
• Add explicit RequestInit annotations so TypeScript validates these objects against the browser fetch API contract.
• Covers the backend JSONL fetch, renderer list refresh, and translation request paths that were intended to send credentials.

Bug

fetch only reads RequestInit.credentials; JavaScript object keys are case-sensitive, so Credentials: 'include' is treated as an unrelated property and silently ignored. For cross-origin deployments this leaves the request at the browser default credentials behavior, so cookies and other credentials are not included even though the server enables credentialed CORS.

Fix

Updated the three affected request option objects:

• src/utils/api-manager.ts JSONL fetch
• src/utils/api-manager.ts renderer list refresh
• src/components/app/request-worker.ts translation request

Each now uses credentials: 'include' and is typed as RequestInit, which prevents future casing or value mistakes from bypassing TypeScript.

Verification

• Searched src for remaining uppercase Credentials: request options; none remain.
• Ran pnpm run build successfully.