fix(accounts): treat SuperGrok Plus as a paid billing plan

[lanting200]

Summary

• xAI now reports Build $100 SuperGrok Plus as subscriptionTier=SuperGrokPlus with weekly numeric limits at 0.
• The paid-plan allowlist only knew SuperGrok / Pro / Heavy / Lite, so those accounts were classified as unknown and dropped out of Super routing.
• Treat supergrokplus as paid, and keep later SuperGrok* plan names paid in both Go and the SQL list filters.

Test plan

• go test ./internal/domain/account ./internal/infra/provider/cli ./internal/infra/persistence/relational
• Import or refresh a Build account whose billing plan_name is SuperGrokPlus and weekly usage is 0%
• Confirm the account list filter quotaType=paid includes it without setting buildSuperEntitled
• Confirm Free / Basic accounts are still classified as free

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