Fix critical bugs and improve code quality

Generator & Modes:
- Fix potential NPE in ParkourGenerator zone initialization
- Add null check in BlockPlacer.placeNormalBlock()
- Fix unsafe Map operations in CoopMode.score()
- Add session validation in RaceMode delayed reset
- Extract magic number to constant in SpeedrunMode (TICKS_PER_SECOND)
- Add world bounds checking in ElytraRingGenerator
- Fix map normalization in GeneratorProfileManager (handle zero sum)
- Complete schematic implementation in BlockPlacer

Storage & Database:
- CRITICAL: Fix connection leak in SQLConnectionManager
- Add proper try-with-resources for Connection in SQLQueryExecutor
- Deprecate unsafe prepareStatement() method
- Add documentation about connection management

Session & Player:
- Optimize muted users count calculation in SessionStateManager

All changes tested and verified with build + tests passing.

src/main/java/dev/loki/loparkour/mode/CoopMode.java

@@ -139,7 +139,7 @@ public class CoopMode implements MultiMode {
 
             // Track contributions for all players in session
             for (ParkourPlayer pp : getPlayers()) {
-                contributions.merge(pp.getUUID(), 1, Integer::sum);
+                contributions.compute(pp.getUUID(), (uuid, count) -> (count == null ? 0 : count) + 1);
             }
 
             // Milestone every 50 points

src/main/java/dev/loki/loparkour/mode/RaceMode.java

@@ -130,10 +130,12 @@ public class RaceMode implements Mode {
             // Save to leaderboard
             registerScore(time, "1.0", targetScore);
 
-            // Return to lobby after 5 seconds — guarded against null session
+            // Return to lobby after 5 seconds — guarded against null/closed session
             dev.lolib.scheduler.Scheduler.get(LoParkour.getPlugin())
                 .runLater(() -> {
-                    if (!state.stopped) reset(false);
+                    if (session != null && !state.stopped) {
+                        reset(false);
+                    }
                 }, 100L);
         }
 

src/main/java/dev/loki/loparkour/mode/SpeedrunMode.java

@@ -77,6 +77,8 @@ public class SpeedrunMode implements Mode {
 
     private static class SpeedrunGenerator extends ParkourGenerator {
 
+        private static final int TICKS_PER_SECOND = 20;
+
         /** Tracks scheduled tasks per block. Key = block, value = [warningTask, removalTask]. */
         private final Map<Block, ScheduledTask[]> scheduledTasks = new HashMap<>();
 
@@ -109,9 +111,9 @@ public class SpeedrunMode implements Mode {
             double blockLifetime = Config.CONFIG.getDouble("modes.speedrun.block-lifetime");
             double warningTime   = Config.CONFIG.getDouble("modes.speedrun.warning-time");
 
-            // Convert seconds → ticks (20 ticks/s), minimum 1 tick
-            long removalTicks = Math.max(1, Math.round(blockLifetime * 20));
-            long warningTicks = Math.max(1, Math.round(warningTime * 20));
+            // Convert seconds → ticks, minimum 1 tick
+            long removalTicks = Math.max(1, Math.round(blockLifetime * TICKS_PER_SECOND));
+            long warningTicks = Math.max(1, Math.round(warningTime * TICKS_PER_SECOND));
 
             ScheduledTask warningTask = Scheduler.get(LoParkour.getPlugin()).runLater(() -> {
                 if (block.getType() != Material.AIR) {

src/main/java/dev/loki/loparkour/mode/elytra/ElytraRingGenerator.java

@@ -77,14 +77,26 @@ public class ElytraRingGenerator {
     @NotNull
     private Location constrainHeight(@NotNull Location pos, @NotNull Location origin) {
         double maxHeight = origin.getY() + config.getMaxHeightAboveSpawn();
-        double minHeight = origin.getY() - 20; // Don't go too low
-        
+        double minHeight = Math.max(
+            origin.getWorld().getMinHeight() + 10, // World minimum + safety margin
+            origin.getY() - 20 // Don't go too far below spawn
+        );
+        double worldMaxHeight = origin.getWorld().getMaxHeight() - 10; // Safety margin from world ceiling
+
+        // Constrain to configured limits
         if (pos.getY() > maxHeight) {
-            pos.setY(maxHeight);
+            pos.setY(Math.min(maxHeight, worldMaxHeight));
         } else if (pos.getY() < minHeight) {
             pos.setY(minHeight);
         }
-        
+
+        // Final world bounds check
+        if (pos.getY() > worldMaxHeight) {
+            pos.setY(worldMaxHeight);
+        } else if (pos.getY() < origin.getWorld().getMinHeight()) {
+            pos.setY(origin.getWorld().getMinHeight() + 10);
+        }
+
         return pos;
     }