Change Set 5: Systems & Sound

A big one. The economy got tuned, the Magnet got scary, and the game found its voice, at least musically.

• Hunter garbage drops now scale by size, the dock takes salvage faster, and tow capacity was raised to 24.
• Added a behind-the-scenes difficulty-lever framework and a standalone scoop-tuning tool.
• Magnet buff: a screen-wide pull with distance falloff, double the duration, and it now grabs clumps too.
• Low-health warning: a looping siren plus a red pointer aimed at the nearest health pickup.
• The music system went live, with a proper scheduler, menu ducking, a title theme, and gameplay tracks that thicken as difficulty ramps.