Skip user upsert when nothing changed to avoid row accumulation

ReplacingMergeTree only deduplicates during background merges, so
every login was inserting a new row even when all fields were identical.
Now compares the existing record and skips the write if nothing changed.

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

cameleer3-server-app/src/main/java/com/cameleer3/server/app/storage/ClickHouseUserRepository.java

@@ -47,11 +47,16 @@ public class ClickHouseUserRepository implements UserRepository {
 
     @Override
     public void upsert(UserInfo user) {
-        // Preserve created_at from existing record on re-login.
-        // ReplacingMergeTree deduplicates by ORDER BY (user_id), keeping the row
-        // with the highest updated_at.
         Optional<UserInfo> existing = findById(user.userId());
         if (existing.isPresent()) {
+            UserInfo ex = existing.get();
+            // Skip write if nothing changed — avoids accumulating un-merged rows
+            if (ex.provider().equals(user.provider())
+                    && ex.email().equals(user.email())
+                    && ex.displayName().equals(user.displayName())
+                    && ex.roles().equals(user.roles())) {
+                return;
+            }
             jdbc.update(
                     "INSERT INTO users (user_id, provider, email, display_name, roles, created_at, updated_at) "
                             + "SELECT user_id, ?, ?, ?, ?, created_at, now64(3, 'UTC') "