feat: gate provider usage candidates

[ictechgy]

Summary

• add an offline aggregate-only provider usage scorer for metered-cost and fixed-subscription quota evidence
• reject no-op economic candidates whose exact command matches the baseline
• keep Codex, agy, and Grok standard routes at medium in the cost-focused scaffolds
• record the rejected Terra-to-Luna Codex qualification without retaining task or response data

Safety boundaries

• no provider credentials, raw exports, task text, responses, or pair rows are persisted
• subscription quota evidence cannot claim monthly bill reduction or feed the cost recommender
• the Luna candidate remains unqualified after two new critical failures; built-in routes are unchanged

Verification

• Python 3.10: 816 tests passed with ResourceWarning as error
• Python 3.14: 816 tests passed with ResourceWarning as error
• Ruff 0.16.2 check and format-check passed
• strict mypy passed for 107 source files
• compileall and git diff --check passed