feat(api-key): add independent quota and expiration support

This feature allows API Keys to have their own quota limits and expiration
times, independent of the user's balance.

Backend:
- Add quota, quota_used, expires_at fields to api_key schema
- Implement IsExpired() and IsQuotaExhausted() checks in middleware
- Add ResetQuota and ClearExpiration API endpoints
- Integrate quota billing in gateway handlers (OpenAI, Anthropic, Gemini)
- Include quota/expiration fields in auth cache for performance
- Expiration check returns 403, quota exhausted returns 429

Frontend:
- Add quota and expiration inputs to key create/edit dialog
- Add quick-select buttons for expiration (+7, +30, +90 days)
- Add reset quota confirmation dialog
- Add expires_at column to keys list
- Add i18n translations for new features (en/zh)

Migration:
- Add 045_add_api_key_quota.sql for new columns

backend/internal/handler/dto/mappers.go

@@ -76,6 +76,9 @@ func APIKeyFromService(k *service.APIKey) *APIKey {
 		Status:      k.Status,
 		IPWhitelist: k.IPWhitelist,
 		IPBlacklist: k.IPBlacklist,
+		Quota:       k.Quota,
+		QuotaUsed:   k.QuotaUsed,
+		ExpiresAt:   k.ExpiresAt,
 		CreatedAt:   k.CreatedAt,
 		UpdatedAt:   k.UpdatedAt,
 		User:        UserFromServiceShallow(k.User),

backend/internal/handler/dto/types.go

@@ -40,6 +40,9 @@ type APIKey struct {
 	Status      string    `json:"status"`
 	IPWhitelist []string  `json:"ip_whitelist"`
 	IPBlacklist []string  `json:"ip_blacklist"`
+	Quota       float64   `json:"quota"`       // Quota limit in USD (0 = unlimited)
+	QuotaUsed   float64   `json:"quota_used"`  // Used quota amount in USD
+	ExpiresAt   *time.Time `json:"expires_at"` // Expiration time (nil = never expires)
 	CreatedAt   time.Time `json:"created_at"`
 	UpdatedAt   time.Time `json:"updated_at"`