feat(subscription): add five-hour usage limits

[paraliine]

Related Issue

Closes #3416

Summary

This PR adds an independent rolling five-hour usage limit to the subscription system.

Changes

• Allow administrators to configure a five-hour USD limit for subscription groups
• Track five-hour usage and window start time for each user subscription
• Enforce the limit during API key authentication and billing
• Accumulate five-hour usage alongside daily, weekly, and monthly usage
• Support manual five-hour quota resets
• Display five-hour usage and reset time in the admin and user interfaces
• Add English and Chinese translations for the new quota fields

The five-hour window starts when the subscription is first used and resets on a rolling five-hour cycle.

Database Changes

Add an optional field to subscription groups:

• five_hour_limit_usd

Add the following fields to user subscriptions:

• five_hour_usage_usd
• five_hour_window_start

Existing subscription groups remain unlimited for the five-hour dimension unless a limit is explicitly configured.

Compatibility

• The five-hour limit is optional and opt-in
• Existing subscription groups retain their current behavior
• API changes are additive
• No existing quota fields or reset behavior are removed

Validation

• Backend unit tests:
  • go test -tags=unit ./internal/service ./internal/repository ./internal/server/...
• Frontend type checking
• Frontend ESLint checks