feat(payment): add balance packages and flexible redeem validity

[laozuzhen]

Summary

• Add balance-package support so wallet balance can be granted with an expiry and deducted before permanent wallet balance.
• Allow redeem-code validity to be represented with sub-day precision and apply it to subscription/balance package redemption flows.
• Extend payment catalog/order handling, XunhuPay provider support, tiered balance pricing, and related admin/user payment UI.

Tests

• go test ./internal/service ./internal/payment ./internal/handler ./internal/handler/admin ./internal/server/routes -run 'Payment|Redeem|BalancePackage|Subscription|Xunhu|Plan|Fulfillment|Order'

Notes

• Frontend build was not run in the isolated worktree because frontend/node_modules is not installed there.

[github-actions]

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[laozuzhen]

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