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>

backend/prisma/schema.prisma

@@ -24,6 +24,7 @@ model Kc {
   guests        GuestAccount[]
   localUsers    User[]
   teamerInvites TeamerInvite[]
+  verantwortlicheInvites VerantwortlicheInvite[]
 }
 
 /// A local congregation/community participating in one Kc.
@@ -37,6 +38,7 @@ model Gemeinde {
   memberships   Membership[]
   guests        GuestAccount[]
   teamerInvites TeamerInvite[]
+  verantwortlicheInvites VerantwortlicheInvite[]
 
   @@unique([kcId, name])
 }
@@ -152,13 +154,42 @@ model TeamerInvite {
   gemeinde Gemeinde @relation(fields: [gemeindeId], references: [id], onDelete: Cascade)
 }
 
+/// Invitation issued by a Leitungsteam member so a person can register as
+/// Gemeinde Verantwortliche/r for a specific Gemeinde via their
+/// Konfi-Castle-ID (Authentik) — skips the self-registration approval step
+/// since a Leitungsteam member is vouching for them directly. A group link
+/// leaves `email` null and may be redeemed up to `maxUses` times (null =
+/// unlimited); a personal invite pins `email` and defaults to a single use.
+model VerantwortlicheInvite {
+  id              String    @id @default(cuid())
+  kcId            String
+  gemeindeId      String
+  token           String    @unique
+  email           String?
+  maxUses         Int?
+  usedCount       Int       @default(0)
+  expiresAt       DateTime?
+  revokedAt       DateTime?
+  createdByUserId String
+  createdAt       DateTime  @default(now())
+
+  kc       Kc       @relation(fields: [kcId], references: [id], onDelete: Cascade)
+  gemeinde Gemeinde @relation(fields: [gemeindeId], references: [id], onDelete: Cascade)
+}
+
 /// A workshop election, scoped to a Kc; name carries a date key + "Teil".
+/// `phasenAnzahl` mirrors the WP plugin's `anzahl_einheiten`: a Wahl can run
+/// several independent phases (e.g. morning/afternoon), each with its own
+/// workshops, its own guest submission, and its own assignment run — a guest
+/// submits once per phase, not once for the whole Wahl.
 model Wahl {
   id               String   @id @default(cuid())
   kcId             String
   name             String
   datumsSchluessel String
   teil             String
+  beschreibung     String?
+  phasenAnzahl     Int      @default(1)
   isOpen           Boolean  @default(true)
   createdAt        DateTime @default(now())
 
@@ -168,10 +199,14 @@ model Wahl {
   forceZuteilungen ForceZuteilung[]
 }
 
+/// A workshop offered in one phase of a Wahl. `phase` is 1-based and must be
+/// <= the owning Wahl's `phasenAnzahl`.
 model Workshop {
   id            String @id @default(cuid())
   wahlId        String
+  phase         Int    @default(1)
   name          String
+  beschreibung  String?
   kapazitaet    Int
   minTeilnehmer Int    @default(0)
 
@@ -180,10 +215,13 @@ model Workshop {
   forceZuteilungen ForceZuteilung[]
 }
 
-/// A participant's submitted choices for a Wahl.
+/// A participant's submitted choices for one phase of a Wahl. A guest submits
+/// separately per phase (matching the WP plugin), so the same guest can have
+/// one row per (wahlId, phase).
 model Teilnehmer {
   id             String   @id @default(cuid())
   wahlId         String
+  phase          Int      @default(1)
   guestAccountId String
   prioritaeten   Json
   createdAt      DateTime @default(now())
@@ -193,7 +231,7 @@ model Teilnehmer {
   zuteilung      Zuteilung?
   forceZuteilung ForceZuteilung?
 
-  @@unique([wahlId, guestAccountId])
+  @@unique([wahlId, guestAccountId, phase])
 }
 
 /// Manual override set by LT before running the assignment algorithm; takes precedence.