feat(auth): add revokeOtherSessions and revokeAllSessions to AuthService

Uses JdbcIndexedSessionRepository (optional field — null-safe in non-web
test contexts) to delete all sessions for a principal except the current
one (revokeOtherSessions) or all sessions unconditionally (revokeAllSessions).
Both methods return the count of deleted sessions for audit payloads.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/auth/AuthService.java

@@ -7,10 +7,12 @@ import org.raddatz.familienarchiv.audit.AuditService;
 import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.user.AppUser;
 import org.raddatz.familienarchiv.user.UserService;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.security.authentication.AuthenticationManager;
 import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.AuthenticationException;
+import org.springframework.session.jdbc.JdbcIndexedSessionRepository;
 import org.springframework.stereotype.Service;
 
 import java.util.Map;
@@ -25,6 +27,9 @@ public class AuthService {
     private final UserService userService;
     private final AuditService auditService;
 
+    @Autowired(required = false)
+    private JdbcIndexedSessionRepository sessionRepository;
+
     /**
      * Validates credentials and returns the authenticated user plus the Spring Security
      * Authentication object. The caller is responsible for persisting the Authentication
@@ -53,6 +58,23 @@ public class AuthService {
         }
     }
 
+    public int revokeOtherSessions(String currentSessionId, String principalName) {
+        int count = 0;
+        for (String id : sessionRepository.findByPrincipalName(principalName).keySet()) {
+            if (!id.equals(currentSessionId)) {
+                sessionRepository.deleteById(id);
+                count++;
+            }
+        }
+        return count;
+    }
+
+    public int revokeAllSessions(String principalName) {
+        var sessions = sessionRepository.findByPrincipalName(principalName);
+        sessions.keySet().forEach(sessionRepository::deleteById);
+        return sessions.size();
+    }
+
     public void logout(String email, String ip, String ua) {
         AppUser user = userService.findByEmail(email);
         auditService.log(AuditKind.LOGOUT, user.getId(), null, Map.of(