feat(chat): free-form GRUPPE channels with mutable participants

- ChatChannelType.GRUPPE: created by Leitungsteam (any KC) or a Gemeinde
  Verantwortliche/r (own KC), mixing team users and guests/Konfis as
  explicit ChatParticipant rows (unlike GEMEINDE_GRUPPE, membership is
  not derived from Gemeinde)
- POST /chat/:kcId/gruppen to create, GET participant-candidates, and
  POST/DELETE /chat/gruppen/:channelId/participants to manage membership
  (creator, LT, or Verantwortliche/r of that KC)
- ChatGateway broadcasts chat:participants-changed on membership change
- PushService updated for nullable ChatParticipant.userId + new
  guestAccountId column
- SyncService now replicates ChatParticipant
- Prisma migration + 14 new unit tests (75/75 passing), tsc clean
- CI: add .gitea/workflows/cybedefend-scan.yml + .cybedefend project config

src/chat/chat.controller.ts

@@ -1,8 +1,10 @@
-import { Body, Controller, Get, Param, Post, Req, UseGuards } from '@nestjs/common';
+import { Body, Controller, Delete, Get, Param, Post, Req, UseGuards } from '@nestjs/common';
 import { AuthGuard } from '@nestjs/passport';
 import { ChatService } from './chat.service';
+import { ChatGateway } from './chat.gateway';
 import { CreateChannelDto } from './dto/create-channel.dto';
 import { CreateDirectChannelDto } from './dto/create-direct-channel.dto';
+import { AddParticipantDto } from './dto/add-participant.dto';
 import { Roles } from '../common/roles.decorator';
 import { RolesGuard } from '../common/roles.guard';
 import { Role } from '../common/role.enum';
@@ -14,7 +16,10 @@ type ChatRequest = AuthenticatedRequest & { user?: AuthenticatedRequest['user']
 
 @Controller('chat')
 export class ChatController {
-  constructor(private readonly chat: ChatService) {}
+  constructor(
+    private readonly chat: ChatService,
+    private readonly gateway: ChatGateway,
+  ) {}
 
   /// Channel administration (Gemeinde-Gruppen, LT-Kanäle, Broadcasts) is Leitungsteam-only.
   @Post(':kcId/channels')
@@ -24,6 +29,73 @@ export class ChatController {
     return this.chat.createChannel(kcId, dto.type, dto.gemeindeId);
   }
 
+  /// Free-form group chat ("Gruppenchat"): a Leitungsteam member (any KC) or
+  /// a Gemeinde Verantwortliche/r (their own KC, enforced by RolesGuard's
+  /// kcId scoping) can create one and pick any mix of team users and Konfis
+  /// (guests) from this KC as initial participants.
+  @Post(':kcId/gruppen')
+  @UseGuards(AuthGuard(['authentik', 'team']), RolesGuard)
+  @Roles(Role.LEITUNGSTEAM, Role.GEMEINDE_VERANTWORTLICHER)
+  createGruppe(
+    @Param('kcId') kcId: string,
+    @Body() dto: CreateChannelDto,
+    @Req() req: AuthenticatedRequest,
+  ) {
+    return this.chat.createGruppe(kcId, dto.name, req.user!.userId, {
+      userIds: dto.participantUserIds,
+      guestIds: dto.participantGuestIds,
+    });
+  }
+
+  /// Candidates (team users + Konfis) a caller may add to a Gruppenchat in
+  /// this KC. Allowed for LT or a Verantwortliche/r of this KC.
+  @Get(':kcId/gruppen/participant-candidates')
+  @UseGuards(AuthGuard(['authentik', 'team']))
+  listPossibleParticipants(@Param('kcId') kcId: string, @Req() req: AuthenticatedRequest) {
+    return this.chat.listPossibleParticipants(kcId, req.user!);
+  }
+
+  /// Add a team user or Konfi to a Gruppenchat. Allowed for the channel's
+  /// creator, any Leitungsteam member, or a Verantwortliche/r of that KC.
+  @Post('gruppen/:channelId/participants')
+  @UseGuards(AuthGuard(['authentik', 'team']))
+  addParticipant(
+    @Param('channelId') channelId: string,
+    @Body() dto: AddParticipantDto,
+    @Req() req: AuthenticatedRequest,
+  ) {
+    return this.chat
+      .addParticipant(
+        channelId,
+        { kind: 'user', user: req.user! },
+        { userId: dto.userId, guestId: dto.guestId },
+      )
+      .then((result) => {
+        this.gateway.notifyParticipantsChanged(channelId);
+        return result;
+      });
+  }
+
+  /// Remove a team user or Konfi from a Gruppenchat. Same authorization as add.
+  @Delete('gruppen/:channelId/participants')
+  @UseGuards(AuthGuard(['authentik', 'team']))
+  removeParticipant(
+    @Param('channelId') channelId: string,
+    @Body() dto: AddParticipantDto,
+    @Req() req: AuthenticatedRequest,
+  ) {
+    return this.chat
+      .removeParticipant(
+        channelId,
+        { kind: 'user', user: req.user! },
+        { userId: dto.userId, guestId: dto.guestId },
+      )
+      .then((result) => {
+        this.gateway.notifyParticipantsChanged(channelId);
+        return result;
+      });
+  }
+
   /// Any two team members of the same KC can start a direct conversation
   /// (Authentik-backed members and local Gemeinde Teamer alike).
   @Post('direct')