Recognize main in coverage contracts

[rmcdaniel]

Summary

• align the coverage checker and its self-test with the renamed main branch
• align the fast unit-only coverage contract with main
• preserve the 100% target, complete source inventory, and raised 85.51% combined baseline

Root cause

Main run 33523090498 correctly rejected the renamed combined contract because the checker still hard-coded v2. The product and database tests all passed; only coverage contract identity failed.

Verification

• coverage-ratchet self-test passes
• PHP syntax check passes
• both coverage contract JSON files parse
• public-boundary scan passes

Contributes to #426.