Fix UI issues: add translations, venues page, remove duplicate SQL files

- Add missing nav.profile and nav.venues translation keys (en/fr/de)
- Add venues listing translations for all 3 languages
- Create /venues page with search, city filter, and venue cards grid
- Add Venues link to nav header (visible to all users)
- Fix hero stats: use dynamic cities/venues counts instead of hardcoded
- Remove data.sql and schema.sql (DbInitializer handles all seeding,
  Hibernate handles schema — these SQL files caused duplicate data)
- Add .venues-grid CSS layout

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

Author: iPwnds

Eventify-Back-End/src/main/resources/data.sql

@@ -320,6 +320,13 @@ header.site-header {
   gap: 0;
 }
 
+/* ===== Venues Grid ===== */
+.venues-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
+  gap: 20px;
+}
+
 /* ===== Venue Card v2 ===== */
 .venue-card-v2 {
   background: var(--card);