fix: return proper type in calculateAndUpdateRequestCost early exit (#915)

The early return when no price data is found was returning undefined
instead of the expected object type. Fixed to return consistent object
structure matching other early returns in the function.

Fixed:
- Type 'undefined' is not assignable to type return object in response-handler.ts:3111

CI Run: https://github.com/ding113/claude-code-hub/actions/runs/23082651541

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <[email protected]>