feat: add "forgot account" reset flow with wallet preservation

Add account reset functionality for users who forgot their login credentials.
The reset clears authentication data while preserving wallet private keys and
exchange configs, which are automatically adopted by the new account on
re-registration to prevent fund loss.

- Add POST /api/reset-account endpoint
- Add "Forgot account?" button on login page (zh/en/id)
- Orphan ai_models and exchanges are re-assigned to new user on register
- Onboarding reuses existing claw402 wallet instead of generating new one

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/handler_onboarding.go

@@ -152,6 +152,7 @@ func (s *Server) handleCurrentBeginnerWallet(c *gin.Context) {
 }
 
 func (s *Server) resolveBeginnerWallet(userID string) (privateKey string, address string, configuredModelID string, reused bool, err error) {
+	// 1. Check if current user already has a claw402 wallet
 	models, err := s.store.AIModel().List(userID)
 	if err != nil {
 		return "", "", "", false, err
@@ -175,6 +176,25 @@ func (s *Server) resolveBeginnerWallet(userID string) (privateKey string, addres
 		return existingKey, addr, model.ID, true, nil
 	}
 
+	// 2. Check for orphan claw402 wallet from a previous account (e.g. after account reset).
+	//    Adopt it to preserve funds.
+	orphan, orphanErr := s.store.AIModel().FindOrphanClaw402()
+	if orphanErr == nil && orphan != nil {
+		existingKey := strings.TrimSpace(orphan.APIKey.String())
+		if existingKey != "" {
+			addr, addrErr := walletAddressFromPrivateKey(existingKey)
+			if addrErr == nil {
+				if adoptErr := s.store.AIModel().AdoptModel(orphan.ID, userID); adoptErr != nil {
+					logger.Warnf("Failed to adopt orphan claw402 wallet for user %s: %v", userID, adoptErr)
+				} else {
+					logger.Infof("✓ Adopted orphan claw402 wallet %s for new user %s (address: %s)", orphan.ID, userID, addr)
+					return existingKey, addr, orphan.ID, true, nil
+				}
+			}
+		}
+	}
+
+	// 3. No existing wallet found — generate a new one
 	privateKeyObj, genErr := gethcrypto.GenerateKey()
 	if genErr != nil {
 		return "", "", "", false, genErr