feat(PT9-383): use server-resolved source from quote response for order building

[edvardg]

Change Summary

What does this PR change?

• SDK now reads the optional source field from the /receive API response
• When building a Fusion order, the response source takes precedence over the request source for salt injection
• Falls back to request source if the API response doesn't include one (backward compat with older API versions)

Changes

File	What changed
types.ts	Added optional source to QuoterResponse
quote/quote.ts	Store response.source, use this.source || this.params.source in createFusionOrder
quoter.api.spec.ts	4 new tests: store from response, undefined when absent, prefer response over request, fallback to request

Backward compatibility

• Fully backward compatible — source is optional in the response type
• Older API versions that don't return source → SDK falls back to this.params.source (existing behavior)
• No breaking changes to public API

Related Issue/Ticket:
https://1inch.atlassian.net/browse/PT9-383

Testing & Verification

How was this tested?

• Unit tests
• Integration tests
• Manual testing (describe steps)
• Verified on staging

Risk Assessment

Risk Level:

• Low - Minor changes, no operational impact
• Medium - Moderate changes, limited impact, standard rollback available
• High - Significant changes, potential operational impact, complex rollback

Risks & Impact