Introduces a new "bonus item" system alongside the existing smashables:
- **Gameplay**: Floating collectible prizes (CTC box, guitar, cash) that the bus passes through with zero physical response. On first contact, the item pops (scale-up + fade) and spawns a radial burst of tinted firework particles that arc down under gravity, settle on terrain, and fade out. Each collected item scores 100 points on the end-of-level tally.
- **Config**: `BONUS_ITEM` in `config.js` holds all tuning knobs (particle count, speed range, spin, lifetime, per-type tint palette, pop scale/duration). `SCORE.perBonusItem` added.
- **Entity**: New `BonusItemManager` class owns static sensor bodies for each bonus item, detects bus collisions, and orchestrates the pop + firework burst animation. Particles are real Matter bodies exempted from bus/kid collision so they can land on terrain without affecting gameplay.
- **Editor**: "Smashables" section renamed to "Placeables" with a kind toggle (Smashables vs Bonus items). Bonus items are float-only with no gravity option. Preview map, click-to-place, item list, and export all support both kinds. `splitPlaceables()` in `levelBuilder.js` splits the unified editor list into the two level arrays (`items` / `bonusItems`).
- **Levels**: Levels 2–6 updated with bonus item placements (and some additional smashable items).
- **Assets**: New `bonus-items.png` spritesheet (9 frames: 3 bonus items × [item + 2 firework objects]) registered in the asset manifest.
- **Score screen**: `_revealBonus()` method in `LevelScoreScene` displays collected bonus count and points, skipped when zero.
- Fix terrain preview aspect ratio to match in-game rendering by using
consistent X/Y scaling, preventing slopes from appearing distorted
- Calculate timeLimit automatically based on level length and pace
(TIME_LIMIT_PACE) to ensure consistent difficulty scaling across levels
- Add max-height and vertical scrolling to the level preview panel
- Generate level02 (The Big Jump) from the editor with manual tweak
- Add `timeLimit` configuration to levels 1-4
- Implement countdown timer that starts when throttle is pressed
- Display remaining time in HUD, turning red when under 10s
- Add 'time-up' failure condition and message in LevelFailedScene
Brian Fertig