feat: Stadium Elite Design, Rangliste, Profil-Team, User-Upsert & n8n Cronjob

- MatchCard + TipModal: Uhrzeit statt VS zwischen Flaggen, Gruppe zentriert
- LeaderboardPage: Podium (2./1./3.), DU-Badge, Trend-Pfeile, Team-Zeile, CTA-Card
- AdminPage: Stadium Elite Redesign mit Result-Bar und Inline-Spinner
- ProfilePage: Team-Feld inline editierbar (PATCH /api/profile/team)
- User-Upsert beim ersten App-Aufruf (Matches-Route) statt erst beim Tipp
- DB Migration 002: team-Spalte in users, Leaderboard View aktualisiert
- Leaderboard-Refresh automatisch nach Tipps-Auswertung
- n8n Workflow angelegt: stündlicher Sync + Auswertung (ID: t3SDspIGDXwkfOt3)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/db/migration_002.sql

@@ -0,0 +1,21 @@
+-- Migration 002: Add team field to users table
+ALTER TABLE users ADD COLUMN IF NOT EXISTS team TEXT;
+
+-- Refresh leaderboard view to include team
+DROP MATERIALIZED VIEW IF EXISTS leaderboard;
+
+CREATE MATERIALIZED VIEW leaderboard AS
+SELECT
+  u.id                                          AS user_id,
+  u.full_name,
+  u.team,
+  RANK() OVER (ORDER BY COALESCE(SUM(t.points), 0) DESC) AS rank,
+  COALESCE(SUM(t.points), 0)                   AS total_points,
+  COUNT(t.id) FILTER (WHERE t.points IS NOT NULL) AS tips_count,
+  COUNT(t.id) FILTER (WHERE t.points = 3)       AS exact_count,
+  COUNT(t.id) FILTER (WHERE t.points = 1)       AS tendency_count
+FROM users u
+LEFT JOIN tips t ON t.user_id = u.id
+GROUP BY u.id, u.full_name, u.team;
+
+CREATE UNIQUE INDEX IF NOT EXISTS leaderboard_user_id_idx ON leaderboard (user_id);