feat: dynamic frontend tenant dropdown

backend/internal/handler/auth_handler.go

@@ -463,6 +463,45 @@ func (h *AuthHandler) VerifySignupCode(c *fiber.Ctx) error {
 }
 
 // Signup - Finalize registration
+func (h *AuthHandler) GetActiveTenants(c *fiber.Ctx) error {
+	if h.TenantService == nil {
+		return errorJSON(c, fiber.StatusServiceUnavailable, "Tenant service unavailable")
+	}
+
+	// List all tenants (we use a large limit for now to get all affiliates)
+	tenants, _, err := h.TenantService.ListTenants(c.Context(), 1000, 0, "")
+	if err != nil {
+		return errorJSON(c, fiber.StatusInternalServerError, "Failed to fetch tenants")
+	}
+
+	type tenantResp struct {
+		ID      string   `json:"id"`
+		Name    string   `json:"name"`
+		Slug    string   `json:"slug"`
+		Type    string   `json:"type"`
+		Domains []string `json:"domains"`
+	}
+
+	var results []tenantResp
+	for _, t := range tenants {
+		if t.Status == domain.TenantStatusActive && (t.Type == domain.TenantTypeCompany || t.Type == domain.TenantTypeCompanyGroup) {
+			var domains []string
+			for _, d := range t.Domains {
+				domains = append(domains, d.Domain)
+			}
+			results = append(results, tenantResp{
+				ID:      t.ID,
+				Name:    t.Name,
+				Slug:    t.Slug,
+				Type:    t.Type,
+				Domains: domains,
+			})
+		}
+	}
+
+	return c.JSON(results)
+}
+
 func (h *AuthHandler) Signup(c *fiber.Ctx) error {
 	var req domain.SignupRequest
 	if err := c.BodyParser(&req); err != nil {