feat(groups): add Claude Code client restriction and session isolation

- Add claude_code_only field to restrict groups to Claude Code clients only
- Add fallback_group_id for non-Claude Code requests to use alternate group
- Implement ClaudeCodeValidator for User-Agent detection
- Add group-level session binding isolation (groupID in Redis key)
- Prevent cross-group sticky session pollution
- Update frontend with Claude Code restriction controls

backend/ent/group/group.go

@@ -49,6 +49,10 @@ const (
 	FieldImagePrice2k = "image_price_2k"
 	// FieldImagePrice4k holds the string denoting the image_price_4k field in the database.
 	FieldImagePrice4k = "image_price_4k"
+	// FieldClaudeCodeOnly holds the string denoting the claude_code_only field in the database.
+	FieldClaudeCodeOnly = "claude_code_only"
+	// FieldFallbackGroupID holds the string denoting the fallback_group_id field in the database.
+	FieldFallbackGroupID = "fallback_group_id"
 	// EdgeAPIKeys holds the string denoting the api_keys edge name in mutations.
 	EdgeAPIKeys = "api_keys"
 	// EdgeRedeemCodes holds the string denoting the redeem_codes edge name in mutations.
@@ -141,6 +145,8 @@ var Columns = []string{
 	FieldImagePrice1k,
 	FieldImagePrice2k,
 	FieldImagePrice4k,
+	FieldClaudeCodeOnly,
+	FieldFallbackGroupID,
 }
 
 var (
@@ -196,6 +202,8 @@ var (
 	SubscriptionTypeValidator func(string) error
 	// DefaultDefaultValidityDays holds the default value on creation for the "default_validity_days" field.
 	DefaultDefaultValidityDays int
+	// DefaultClaudeCodeOnly holds the default value on creation for the "claude_code_only" field.
+	DefaultClaudeCodeOnly bool
 )
 
 // OrderOption defines the ordering options for the Group queries.
@@ -291,6 +299,16 @@ func ByImagePrice4k(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldImagePrice4k, opts...).ToFunc()
 }
 
+// ByClaudeCodeOnly orders the results by the claude_code_only field.
+func ByClaudeCodeOnly(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldClaudeCodeOnly, opts...).ToFunc()
+}
+
+// ByFallbackGroupID orders the results by the fallback_group_id field.
+func ByFallbackGroupID(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldFallbackGroupID, opts...).ToFunc()
+}
+
 // ByAPIKeysCount orders the results by api_keys count.
 func ByAPIKeysCount(opts ...sql.OrderTermOption) OrderOption {
 	return func(s *sql.Selector) {