Implement the 025-display-initiative feature that adds initiative modifier and passive initiative display to creature stat blocks, calculated as DEX modifier + (proficiency multiplier × proficiency bonus) from bestiary data, shown in MM 2024 format on the AC line

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/025-display-initiative/quickstart.md

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+# Quickstart: Display Initiative
+
+## Overview
+
+Add initiative display to creature stat blocks. Three layers touched:
+
+1. **Domain**: New `calculateInitiative` pure function + `initiativeProficiency` field on `Creature`
+2. **Adapter**: Parse `initiative.proficiency` from raw 5etools JSON
+3. **UI**: Show "Initiative +X (Y)" next to AC in stat block header
+
+## Key Files
+
+| File | Change |
+|------|--------|
+| `packages/domain/src/creature-types.ts` | Add `initiativeProficiency: number` to `Creature` |
+| `packages/domain/src/initiative.ts` | New file: `calculateInitiative`, `formatInitiativeModifier` |
+| `packages/domain/src/index.ts` | Export new function/types |
+| `packages/domain/src/__tests__/initiative.test.ts` | New file: unit tests |
+| `apps/web/src/adapters/bestiary-adapter.ts` | Parse `initiative.proficiency` from raw JSON |
+| `apps/web/src/components/stat-block.tsx` | Display initiative in header |
+
+## Implementation Order
+
+1. Add `initiativeProficiency` to `Creature` type
+2. Create `calculateInitiative` + `formatInitiativeModifier` in domain with tests
+3. Update bestiary adapter to parse initiative proficiency
+4. Update stat block component to display initiative
+
+## Verification
+
+```bash
+pnpm check  # Must pass — knip + format + lint + typecheck + test
+```
+
+Spot-check: Aboleth should display "Initiative +7 (17)".