fix(player): restore missing additional save timer and reduce autosave interval

The m_additionalSaveTimer was never processed in the update loop, so quick
partial saves after important events (rare+ item pickups, quest completions)
never fired. This caused players to lose progress on disconnect/crash since
only the 15-minute full autosave protected them.

- Add m_additionalSaveTimer tick logic to Player::Update
- Reduce default PlayerSaveInterval from 900000 (15 min) to 300000 (5 min)

Co-authored-by: Cursor <cursoragent@cursor.com>

src/server/apps/worldserver/worldserver.conf.dist

@@ -1753,9 +1753,9 @@ InstantLogout = 1
 #
 #    PlayerSaveInterval
 #        Description: Time (in milliseconds) for player save interval.
-#        Default:     900000 - (15 min)
+#        Default:     300000 - (5 min)
 
-PlayerSaveInterval = 900000
+PlayerSaveInterval = 300000
 
 #
 #    PlayerSave.Stats.MinLevel