Lead search by name returns no results when first and last name are in different fields

[anshulpahwa]

Bug Report

Reported by: @Maya-chen (Sales Ops)

When using the lead list search, filtering by a rep's name like "John" returns zero results even though leads named "John Smith" clearly exist in the system.

Steps to reproduce:

1. Create a lead with first_name="John", last_name="Smith"
2. GET /api/leads/?name=John
3. Expected: lead appears in results
4. Actual: empty list

Root cause hint: The filtering logic in the list view may be using the wrong boolean operator when combining first/last name conditions.

Acceptance criteria:

• GET /api/leads/?name=John returns all leads where either first name OR last name contains "John"
• Add or update a test asserting the correct results for a partial-name search
• Existing tests should continue to pass