feat(auth): invite links for several people, invite by email, registration with approval or email domains

- Invites: link /?invite=CODE, copy link, send by email, max uses with counter
- Registration modes closed | approval | domain | domain+approval | open, waiting list with approve/reject
- REGISTRATION_MODE / REGISTRATION_DOMAINS lock the admin setting; ALLOW_REGISTRATION=true is honoured

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/handlers_admin.go

@@ -8,6 +8,7 @@ import (
 	"github.com/go-chi/chi/v5"
 	"github.com/sandrodach/mindsift/internal/auth"
 	"github.com/sandrodach/mindsift/internal/domain"
+	"github.com/sandrodach/mindsift/internal/storage"
 )
 
 // --- ORGANIZATIONS & TEAMS ---
@@ -93,6 +94,10 @@ func (s *Server) handleAdminGetUsers(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, err.Error())
 		return
 	}
+	pending := s.store.PendingRegistrationIDs()
+	for i := range users {
+		users[i].PendingApproval = pending[users[i].ID]
+	}
 	writeJSON(w, http.StatusOK, users)
 }
 
@@ -191,6 +196,9 @@ func (s *Server) handleAdminUpdateUser(w http.ResponseWriter, r *http.Request) {
 	if req.IsActive != nil && !*req.IsActive {
 		s.wsHub.DisconnectUser(targetUserID)
 	}
+	if req.IsActive != nil && *req.IsActive {
+		s.store.ClearPendingRegistration(targetUserID) // activating by hand counts as approval
+	}
 	writeJSON(w, http.StatusOK, u)
 }
 
@@ -247,6 +255,7 @@ func (s *Server) handleAdminDeleteUser(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	s.removeUserBackups(targetUserID)
+	s.store.ClearPendingRegistration(targetUserID)
 	writeJSON(w, http.StatusOK, map[string]bool{"deleted": true})
 }
 
@@ -270,6 +279,7 @@ func (s *Server) handleAdminCreateInvite(w http.ResponseWriter, r *http.Request)
 		Role           string `json:"role"`
 		OrganizationID string `json:"organizationId"`
 		ValidDays      int    `json:"validDays"`
+		MaxUses        int    `json:"maxUses"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültiges JSON")
@@ -278,7 +288,7 @@ func (s *Server) handleAdminCreateInvite(w http.ResponseWriter, r *http.Request)
 	if req.Role == "admin" && (caller == nil || caller.Role != "admin") {
 		req.Role = "member"
 	}
-	inv, err := s.store.CreateUserInvite(callerID, req.Email, req.Role, req.OrganizationID, req.ValidDays)
+	inv, err := s.store.CreateUserInvite(callerID, req.Email, req.Role, req.OrganizationID, req.ValidDays, req.MaxUses)
 	if err != nil {
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
@@ -312,6 +322,16 @@ func (s *Server) settingsForBrowser(settings *domain.SystemSettings) *domain.Sys
 	out.SMTPPassSet = out.SMTPPass != ""
 	out.SMTPPass = ""
 	out.SMTPConfiguredViaEnv = strings.TrimSpace(s.cfg.SMTPHost) != ""
+	// What the environment fixes is shown as in effect and locked in the form
+	if s.cfg.RegistrationMode != "" {
+		out.RegistrationMode = s.cfg.RegistrationMode
+		out.AllowRegistration = out.RegistrationMode == storage.RegistrationOpen
+		out.RegistrationConfiguredViaEnv = true
+	}
+	if s.cfg.RegistrationDomains != "" {
+		out.RegistrationDomains = strings.Join(storage.ParseEmailDomains(s.cfg.RegistrationDomains), ", ")
+		out.RegistrationConfiguredViaEnv = true
+	}
 	return &out
 }
 
@@ -327,6 +347,17 @@ func (s *Server) handleAdminUpdateSettings(w http.ResponseWriter, r *http.Reques
 			settings.SMTPPass = cur.SMTPPass
 		}
 	}
+	// Registration fixed by the environment cannot be changed here (the stored value stays as it was)
+	if s.cfg.RegistrationMode != "" || s.cfg.RegistrationDomains != "" {
+		if cur, err := s.store.GetSystemSettings(); err == nil {
+			if s.cfg.RegistrationMode != "" {
+				settings.RegistrationMode, settings.AllowRegistration = cur.RegistrationMode, cur.AllowRegistration
+			}
+			if s.cfg.RegistrationDomains != "" {
+				settings.RegistrationDomains = cur.RegistrationDomains
+			}
+		}
+	}
 	previousMode := s.store.SharingMode()
 	if err := s.store.UpdateSystemSettings(&settings); err != nil {
 		writeError(w, http.StatusInternalServerError, err.Error())