feat: enabling user search using user phone number

Summary

Extend GET /api/v1/users/{user_identifier} to support searching users by phone number in addition to username and userId.

---

Changes

• Add phoneNumber to search criteria
• Normalize phone numbers before search
• Update API documentation

---

Expected Behavior

• Searching by phone number returns matching users
• Username and userId search continues to work unchanged

---

Impact

• Improves user discoverability via phone number
• Potential privacy concerns if phone numbers are exposed

---

Acceptance Criteria

• Search works with full phone number
• Existing search (username/userId) unaffected
• Phone number normalization handled correctly
• No performance regression