feat(calendar): add domain field and test-connection button to Exchange sources

- Prisma: domain String? added to CalendarSource model (db push applied)
- DTOs: domain in CreateCalendarSourceDto, UpdateCalendarSourceDto, new TestCalendarSourceConfigDto
- Service: domain in SOURCE_SAFE_SELECT, addSource, updateSource; new testConnectionFromConfig method
- Controller: POST /calendar/sources/test-config (before :id routes to avoid collision)
- ExchangeProvider: domain in all source interfaces; passed as 3rd arg to EWS WebCredentials
- Frontend: domain in CalendarSource/CreateSourcePayload/UpdateSourcePayload; testSourceConfig API fn
- Form: domain field (Exchange-only), "Test connection" button with idle/loading/success/error states
- i18n: de+en keys for formFieldDomain, formFieldDomainHint, formTestConnection, formTesting, formTestSuccess, formTestFailed

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

apps/api/src/calendar/calendar.service.ts

@@ -8,6 +8,7 @@ import { PrismaService } from '../prisma/prisma.service';
 import { CalendarCryptoService } from './crypto.service';
 import { CreateCalendarSourceDto } from './dto/create-calendar-source.dto';
 import { UpdateCalendarSourceDto } from './dto/update-calendar-source.dto';
+import { TestCalendarSourceConfigDto } from './dto/test-calendar-source-config.dto';
 import { ICSProvider } from './providers/ics.provider';
 import { CalDAVProvider } from './providers/caldav.provider';
 import { ExchangeProvider } from './providers/exchange.provider';
@@ -33,13 +34,13 @@ export interface CalendarEvent {
  */
 export interface CalendarProvider {
   fetchEvents(
-    source: { url: string; username?: string; password?: string; exchangeMode?: string | null; id: string; color?: string | null },
+    source: { url: string; username?: string; password?: string; exchangeMode?: string | null; domain?: string; id: string; color?: string | null },
     from: Date,
     to: Date,
   ): Promise<CalendarEvent[]>;
 
   testConnection(
-    source: { url: string; username?: string; password?: string; exchangeMode?: string | null; id: string },
+    source: { url: string; username?: string; password?: string; exchangeMode?: string | null; domain?: string; id: string },
   ): Promise<boolean>;
 }
 
@@ -54,6 +55,7 @@ const SOURCE_SAFE_SELECT = {
   name: true,
   type: true,
   exchangeMode: true,
+  domain: true,
   url: true,
   username: true,
   // encryptedPassword: NEVER included — T-05-09
@@ -149,6 +151,7 @@ export class CalendarService {
       url: dto.url,
       username: dto.username ?? null,
       exchangeMode: dto.exchangeMode ?? null,
+      domain: dto.domain ?? null,
       color: dto.color ?? '#3B82F6',
     };
 
@@ -191,6 +194,7 @@ export class CalendarService {
     if (dto.url !== undefined) data.url = dto.url;
     if (dto.username !== undefined) data.username = dto.username;
     if (dto.exchangeMode !== undefined) data.exchangeMode = dto.exchangeMode;
+    if (dto.domain !== undefined) data.domain = dto.domain;
     if (dto.color !== undefined) data.color = dto.color;
     if (dto.isVisible !== undefined) data.isVisible = dto.isVisible;
 
@@ -250,6 +254,7 @@ export class CalendarService {
         ? this.crypto.decrypt(source.encryptedPassword)
         : undefined,
       exchangeMode: source.exchangeMode,
+      domain: source.domain ?? undefined,
       id: source.id,
     };
 
@@ -275,6 +280,33 @@ export class CalendarService {
     }
   }
 
+  /**
+   * Tests a calendar source configuration without saving it to the database.
+   * Used by the "Test connection" button in the form before the source is created.
+   */
+  async testConnectionFromConfig(
+    dto: TestCalendarSourceConfigDto,
+  ): Promise<{ success: boolean; error?: string }> {
+    await this.validateUrlNotPrivate(dto.url);
+
+    const provider = this.getProvider(dto.type);
+    const tempSource = {
+      url: dto.url,
+      username: dto.username,
+      password: dto.password,
+      exchangeMode: dto.exchangeMode ?? null,
+      domain: dto.domain,
+      id: 'test-config',
+    };
+
+    try {
+      const success = await provider.testConnection(tempSource);
+      return { success };
+    } catch {
+      return { success: false, error: 'Connection failed' };
+    }
+  }
+
   /**
    * Aggregate events from all visible sources for a user (CAL-02/CAL-03).
    *
@@ -335,6 +367,7 @@ export class CalendarService {
             ? this.crypto.decrypt(source.encryptedPassword)
             : undefined,
           exchangeMode: source.exchangeMode,
+          domain: source.domain ?? undefined,
           id: source.id,
           color: source.color,
         };