fix(enterprise): guard against null domains and trim whitespace in HRD screen

[ankita10119]

Changes

connection/enterprise.js

• matchConnection: added null guard on x.get('domains') before calling .contains() - prevents a crash when a connection has no domains configured
• findADConnectionWithoutDomain: same null guard before calling .isEmpty()

connection/enterprise/hrd_screen.jsx

• Changed domain !== null to domain && domain.trim() - empty or whitespace-only domain strings now fall back to the generic login instructions instead of interpolating a blank value into the enterprise instructions string

References

• Backport of changes from fix: resolve null domain handling and v13 lock bug fixes #2807

Testing

• This change adds unit test coverage
• This change adds integration test coverage
• This change has been tested on the latest version of the platform/language

New test file matchConnection.test.js covers:

• Matching a connection by email domain
• No match when domain differs
• No throw when a connection has null domains
• Returns false for an email with no domain part

hrd_screen.test.js adds two new cases:

• Empty string domain falls back to generic instructions
• Whitespace-only domain falls back to generic instructions

All 407 tests pass.

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All code quality tools/guidelines have been run/followed
• All relevant assets have been compiled