feat(api-key): add IP whitelist/blacklist restriction and usage log IP tracking

- Add IP restriction feature for API keys (whitelist/blacklist with CIDR support)
- Add IP address logging to usage logs (admin-only visibility)
- Remove billing_type column from usage logs UI (redundant)
- Use generic "Access denied" error message for security

Backend:
- New ip package with IP/CIDR validation and matching utilities
- Database migrations for ip_whitelist, ip_blacklist (api_keys) and ip_address (usage_logs)
- Middleware IP restriction check after API key validation
- Input validation for IP/CIDR patterns on create/update

Frontend:
- API key form with enable toggle for IP restriction
- Shield icon indicator in table for keys with IP restriction
- Removed billing_type filter and column from usage views

backend/ent/usagelog/usagelog.go

@@ -64,6 +64,8 @@ const (
 	FieldFirstTokenMs = "first_token_ms"
 	// FieldUserAgent holds the string denoting the user_agent field in the database.
 	FieldUserAgent = "user_agent"
+	// FieldIPAddress holds the string denoting the ip_address field in the database.
+	FieldIPAddress = "ip_address"
 	// FieldImageCount holds the string denoting the image_count field in the database.
 	FieldImageCount = "image_count"
 	// FieldImageSize holds the string denoting the image_size field in the database.
@@ -147,6 +149,7 @@ var Columns = []string{
 	FieldDurationMs,
 	FieldFirstTokenMs,
 	FieldUserAgent,
+	FieldIPAddress,
 	FieldImageCount,
 	FieldImageSize,
 	FieldCreatedAt,
@@ -199,6 +202,8 @@ var (
 	DefaultStream bool
 	// UserAgentValidator is a validator for the "user_agent" field. It is called by the builders before save.
 	UserAgentValidator func(string) error
+	// IPAddressValidator is a validator for the "ip_address" field. It is called by the builders before save.
+	IPAddressValidator func(string) error
 	// DefaultImageCount holds the default value on creation for the "image_count" field.
 	DefaultImageCount int
 	// ImageSizeValidator is a validator for the "image_size" field. It is called by the builders before save.
@@ -340,6 +345,11 @@ func ByUserAgent(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldUserAgent, opts...).ToFunc()
 }
 
+// ByIPAddress orders the results by the ip_address field.
+func ByIPAddress(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldIPAddress, opts...).ToFunc()
+}
+
 // ByImageCount orders the results by the image_count field.
 func ByImageCount(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldImageCount, opts...).ToFunc()

backend/ent/usagelog/where.go

@@ -180,6 +180,11 @@ func UserAgent(v string) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldEQ(FieldUserAgent, v))
 }
 
+// IPAddress applies equality check predicate on the "ip_address" field. It's identical to IPAddressEQ.
+func IPAddress(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldEQ(FieldIPAddress, v))
+}
+
 // ImageCount applies equality check predicate on the "image_count" field. It's identical to ImageCountEQ.
 func ImageCount(v int) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldEQ(FieldImageCount, v))
@@ -1190,6 +1195,81 @@ func UserAgentContainsFold(v string) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldContainsFold(FieldUserAgent, v))
 }
 
+// IPAddressEQ applies the EQ predicate on the "ip_address" field.
+func IPAddressEQ(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldEQ(FieldIPAddress, v))
+}
+
+// IPAddressNEQ applies the NEQ predicate on the "ip_address" field.
+func IPAddressNEQ(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldNEQ(FieldIPAddress, v))
+}
+
+// IPAddressIn applies the In predicate on the "ip_address" field.
+func IPAddressIn(vs ...string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldIn(FieldIPAddress, vs...))
+}
+
+// IPAddressNotIn applies the NotIn predicate on the "ip_address" field.
+func IPAddressNotIn(vs ...string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldNotIn(FieldIPAddress, vs...))
+}
+
+// IPAddressGT applies the GT predicate on the "ip_address" field.
+func IPAddressGT(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldGT(FieldIPAddress, v))
+}
+
+// IPAddressGTE applies the GTE predicate on the "ip_address" field.
+func IPAddressGTE(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldGTE(FieldIPAddress, v))
+}
+
+// IPAddressLT applies the LT predicate on the "ip_address" field.
+func IPAddressLT(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldLT(FieldIPAddress, v))
+}
+
+// IPAddressLTE applies the LTE predicate on the "ip_address" field.
+func IPAddressLTE(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldLTE(FieldIPAddress, v))
+}
+
+// IPAddressContains applies the Contains predicate on the "ip_address" field.
+func IPAddressContains(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldContains(FieldIPAddress, v))
+}
+
+// IPAddressHasPrefix applies the HasPrefix predicate on the "ip_address" field.
+func IPAddressHasPrefix(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldHasPrefix(FieldIPAddress, v))
+}
+
+// IPAddressHasSuffix applies the HasSuffix predicate on the "ip_address" field.
+func IPAddressHasSuffix(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldHasSuffix(FieldIPAddress, v))
+}
+
+// IPAddressIsNil applies the IsNil predicate on the "ip_address" field.
+func IPAddressIsNil() predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldIsNull(FieldIPAddress))
+}
+
+// IPAddressNotNil applies the NotNil predicate on the "ip_address" field.
+func IPAddressNotNil() predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldNotNull(FieldIPAddress))
+}
+
+// IPAddressEqualFold applies the EqualFold predicate on the "ip_address" field.
+func IPAddressEqualFold(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldEqualFold(FieldIPAddress, v))
+}
+
+// IPAddressContainsFold applies the ContainsFold predicate on the "ip_address" field.
+func IPAddressContainsFold(v string) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldContainsFold(FieldIPAddress, v))
+}
+
 // ImageCountEQ applies the EQ predicate on the "image_count" field.
 func ImageCountEQ(v int) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldEQ(FieldImageCount, v))