feat(backend): Wahl-Phasen, Verantwortliche-Invites, Auth fixes

- New VerantwortlicheInvite model: LT-issued invites so a person can
  register as Gemeinde Verantwortliche(r) for a specific Gemeinde,
  skipping the self-registration approval step.
- Wahl/Workshop/Teilnehmer gain phase support (phasenAnzahl,
  beschreibung), mirroring the WP plugin's multi-phase elections.
  Teilnehmer unique constraint now scoped per phase.
- Auth: team login + guest auth adjustments, spec coverage.
- sync.service.ts: register VerantwortlicheInvite as a synced model.
- wahl.service.ts: submitTeilnehmer updated for the new phase-scoped
  unique key.
- client: login/home screen rework, new theme.dart, FCM web tweaks.
- .gitignore: ignore .DS_Store.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/auth/dto/team-login.dto.ts

@@ -1,8 +1,19 @@
-import { IsEmail, IsNotEmpty, IsString } from 'class-validator';
+import { IsEmail, IsNotEmpty, IsOptional, IsString } from 'class-validator';
 
+/// Team login accepts EITHER an email (legacy/personal Verantwortliche
+/// accounts) OR a Gemeinde name (the normal Teamer login path, since a
+/// Teamer thinks of their login as "meine Gemeinde", not their email).
+/// At least one of email/gemeindeName is required; enforced in the
+/// controller rather than a custom validator to keep this DTO simple.
 export class TeamLoginDto {
+  @IsOptional()
   @IsEmail()
-  email!: string;
+  email?: string;
+
+  @IsOptional()
+  @IsString()
+  @IsNotEmpty()
+  gemeindeName?: string;
 
   @IsString()
   @IsNotEmpty()