Make UserCred teleport prior verification-neutral

[cmdr-chara]

Summary

• make the uniform UserCred V2 teleport prior include every eligible non-near-zero account equally
• remove Premium and verification fields from the UserCred input projection
• preserve engagement-derived teleport mass and beta blending
• sanitize invalid mass before normalization and add neutral-prior metrics/tests

Why

Subscription and verification status should not provide structural prior mass in an account-credibility score used by downstream systems.

Verification

• scanned UserCred V2 for remaining Premium/verification field dependencies
• added eligibility, near-zero, finite-positive, and invalid-mass tests
• git diff --check / git show --check

The public UserCred snapshot has no Scala build target and this environment has no Scala toolchain, so the added tests could not be executed locally.