Fix camera judder on fast ascent

Root cause: startFollow used lerpY=0.05 + roundPixels=true. At rocket
velocity (~1400 px/s) the camera lagged ~466px behind the player, then
snapped in chunks every frame, giving the impression of low FPS / shake.

Fix:
- Replace startFollow with manual upward-only camera tracking that
  matches the player exactly (doodle-jump standard behavior)
- Disable camera roundPixels so antialiasing actually smooths motion
- Round bg tilePositionY to integer to avoid grid texture shimmer
- Slightly thin out boost effects (flame 3->2/frame, speed line 40->65ms)
  to keep frame budget headroom on weaker devices

src/managers/EffectsManager.js

@@ -21,7 +21,7 @@ export class EffectsManager {
       else this._spawnWind(player);
 
       this.speedLineTimer += delta;
-      if (this.speedLineTimer > 40) {
+      if (this.speedLineTimer > 65) {
         this.speedLineTimer = 0;
         this._spawnSpeedLine();
       }
@@ -70,7 +70,7 @@ export class EffectsManager {
 
   _spawnFlame(player) {
     const baseY = player.y + player.displayHeight / 2 - 6;
-    const count = 3;
+    const count = 2;
     for (let i = 0; i < count; i++) {
       const jitter = Phaser.Math.Between(-9, 9);
       const color = Phaser.Utils.Array.GetRandom(FLAME_COLORS);