feat(01-02): implement compute-applicable-steps (D-10 step ordering)

Task 5 GREEN phase. Pure function returning ordered StepKind[] for a
level-up wizard, conditional on:
- targetLevel (boost levels, skill-increase levels, even/odd)
- hasFreeArchetype (D-13)
- isCaster (D-18)
- classProgressionHasChoiceType (D-19)

Step ordering per D-10:
  class-features → class-feature-choice → boost → skill-increase
  → feat-class/feat-skill (even levels) → feat-general (3,7,11,15,19)
  → feat-ancestry (5,9,13,17) → feat-archetype → spellcaster → review

Invariants: always starts with class-features, always ends with review.
13 tests passing.

server/src/modules/leveling/lib/compute-applicable-steps.ts

@@ -0,0 +1,67 @@
+/**
+ * Pure function — given the level-up parameters, returns the ordered list of
+ * wizard step kinds the player must walk through (D-10 step ordering).
+ *
+ * No NestJS, no Prisma, no I/O. Output is fully determined by inputs.
+ */
+import type { StepKind } from './types';
+
+export interface ComputeStepsInput {
+  targetLevel: number;
+  className: string;
+  hasFreeArchetype: boolean;
+  isCaster: boolean;
+  isSpontaneousCaster: boolean;
+  classProgressionHasChoiceType: boolean;
+}
+
+/** PF2e ability-boost levels (every 5th level after 5). */
+const BOOST_LEVELS: ReadonlySet<number> = new Set([5, 10, 15, 20]);
+
+/** PF2e skill-increase steps (level 3 and every 2 levels thereafter). */
+const SKILL_INCREASE_LEVELS: ReadonlySet<number> = new Set([3, 5, 7, 9, 11, 13, 15, 17, 19]);
+
+/** General-feat slot levels (PF2e CRB). */
+const GENERAL_FEAT_LEVELS: ReadonlySet<number> = new Set([3, 7, 11, 15, 19]);
+
+/**
+ * Ancestry-feat slot levels (PF2e CRB) — character creation grants level 1, but
+ * this function is for level-ups (1 is excluded by callers / handled below).
+ */
+const ANCESTRY_FEAT_LEVELS: ReadonlySet<number> = new Set([1, 5, 9, 13, 17]);
+
+/**
+ * Returns the ordered list of wizard step kinds for a level-up.
+ * Step ordering follows D-10:
+ *   class-features → class-feature-choice (if any)
+ *   → boost (if level ∈ {5,10,15,20})
+ *   → skill-increase (if level ∈ {3,5,7,...,19})
+ *   → feat-class (if even level)
+ *   → feat-skill (if even level)
+ *   → feat-general (if level ∈ {3,7,11,15,19})
+ *   → feat-ancestry (if level ∈ {5,9,13,17}; excludes L1)
+ *   → feat-archetype (if hasFreeArchetype)
+ *   → spellcaster (if isCaster)
+ *   → review
+ */
+export function computeApplicableSteps(input: ComputeStepsInput): StepKind[] {
+  const { targetLevel, hasFreeArchetype, isCaster, classProgressionHasChoiceType } = input;
+  const steps: StepKind[] = ['class-features'];
+
+  if (classProgressionHasChoiceType) steps.push('class-feature-choice');
+  if (BOOST_LEVELS.has(targetLevel)) steps.push('boost');
+  if (SKILL_INCREASE_LEVELS.has(targetLevel)) steps.push('skill-increase');
+  if (targetLevel % 2 === 0) {
+    steps.push('feat-class');
+    steps.push('feat-skill');
+  }
+  if (GENERAL_FEAT_LEVELS.has(targetLevel)) steps.push('feat-general');
+  if (ANCESTRY_FEAT_LEVELS.has(targetLevel) && targetLevel !== 1) {
+    steps.push('feat-ancestry');
+  }
+  if (hasFreeArchetype) steps.push('feat-archetype');
+  if (isCaster) steps.push('spellcaster');
+
+  steps.push('review');
+  return steps;
+}