T7: Fire module for bullets

[Jon-Gear]

Parent

Restructure spec: #13 (RESTRUCTURE_PLAN.md)

What to build

A single firing path where spread and count are data, not subclassed behavior; player and enemy weapons share it; projectiles spawn into the level's own container rather than a global one; bullet physics and hit detection are untouched. Firing, spread, and shot-delay behavior stays identical, and the fire module's placement math is testable headlessly.

Acceptance criteria

• Player and gunner firing, spread patterns, and shot delays behave exactly as they do today
• The spread subclass is removed; a fire spec (count, spread, tag) drives placement
• Tests cover the fire module's bullet-placement math

Blocked by

• T6 Weapon switching and ammo through a service (T6: Weapon switching and ammo through a service #19)