feat: Shot spillover; Speed force; scr_shoot refactor

[EttyKitty]

Summary by cubic

Adds shot spillover across enemy ranks and formations and introduces the Speed Force sweep attack, producing a single consolidated volley. Refactors scr_shoot into modular helpers and splits enemy/player flows for clearer damage, AP, and cleanup.

• New Features

  • Shot spillover: excess damage rolls to the next alive rank (prefers same vehicle type), then the nearest formation behind; cleans up and destroys emptied formations after the volley.
  • Speed Force: sweeps the whole field via scr_shoot_spread (bypasses range/targeting), allocates shots by rank size, and reports one volley; auto-added to bike stacks with an optional ranged variant.
  • Helpers: find_next_alive_rank, get_next_enemy_formation, combat_apply_rank_damage, combat_rank_armour, and formation cleanup; scr_clean now uses combat_rank_armour.

• Bug Fixes

  • Correct AP application for infantry and vehicles; Heretics only get a damage boost (no AP boost).
  • Fixed legacy emplacement weapons (negative indices) so they reliably fire.

^{Written for commit 19170ee. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 3 files

Confidence score: 5/5

• Safe to merge after the addressed issues were fixed.

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

2 issues found across 1 file (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

0 issues found across 1 file (changes from recent commits).

_{Re-trigger cubic}