[E-PF2E-1] Core roll and degrees of success

[alxjrvs]

Part of #942

Phase 1: Core roll and degrees of success

Updated 2026-03-24: Game packages now use .randsum.json specs + codegen, not standalone TypeScript packages. See existing games in packages/games/ for the pattern.

Scope

Implement the PF2e core roll mechanic: 1d20 + modifier vs DC, with full degrees of success including the natural 1/20 shift rule.

Acceptance Criteria

• pf2e.randsum.json spec in packages/games/ expressing 1d20 + modifier vs DC
• Codegen produces src/pf2e.generated.ts — accessible via import { roll } from '@randsum/games/pf2e'
• DegreeOfSuccess result values: CRITICAL_SUCCESS, SUCCESS, FAILURE, CRITICAL_FAILURE
• Degree calculation: beat DC by 10+ -> Critical Success; meet or beat -> Success; miss by 1-9 -> Failure; miss by 10+ -> Critical Failure
• Natural 20 shifts degree up one (clamped at Critical Success)
• Natural 1 shifts degree down one (clamped at Critical Failure)
• Edge cases: nat 20 on already-Critical-Success (no-op), nat 1 on Critical-Failure (no-op), nat 1 overriding a DC+10 beat (resolves to Success)
• Result includes human-readable description alongside degree value
• Spec validated against boundary test cases: exactly DC, DC+-9, DC+-10

Mechanics Reference

• Beat DC by 10+: Critical Success
• Meet or beat DC: Success
• Miss DC by 1-9: Failure
• Miss DC by 10+: Critical Failure
• Natural 20: shift result one step up
• Natural 1: shift result one step down
• Shifts are clamped

Out of Scope

• MAP (Phase 2, [E-PF2E-2] Multiple Attack Penalty (MAP) #967)
• Hero point reroll (Phase 3, [E-PF2E-3] Fortune/Misfortune and Hero Point reroll #968)
• Fortune/Misfortune (Phase 3, [E-PF2E-3] Fortune/Misfortune and Hero Point reroll #968)
• Incapacitation trait