Add tutor availability overlap hints to matching screen

[Taleef7]

Context

The current matching query filters approved tutors by subject and level, but docs/plan-CorvEd.md notes that it does not compare tutor availability windows against the student's requested availability.

Acceptance criteria

• Matching screen highlights overlap between request availability and tutor availability when both are structured windows.
• Non-overlap and missing-availability states are visually clear.
• The feature remains an admin aid, not automated assignment.
• Add tests for overlap helper logic if extracted.

References

• docs/plan-CorvEd.md section 3.2
• Related closed issue: T7.2 matching screen: #48