Initial TTRPG character meta-builder with visual sheet editor.

Offline Electron app seeds 10 system presets, supports create-from-scratch designer with palette/drag/resize/bricks, and exports .ttrpg-system.json for the player.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/testing.md

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+# Testing
+
+## Layers
+
+- **Unit** (`tsx --test`): `app/shared/*` — formula, derived, creation, snapshot, system validate
+- **Integration**: SQLite store (builder), GameSystemsStore (player)
+- **E2E** (Playwright Electron): functional asserts — not smoke-only (see plan)
+
+## Commands
+
+```bash
+# builder
+npm test
+npm run test:e2e   # when e2e suite is added
+
+# player (meta_builder)
+npx tsx --test app/main/gameSystems/gameSystemsStore.test.ts
+npx tsx --test app/shared/characterSheet/core.test.ts
+```
+
+## Preset smoke
+
+```bash
+node scripts/preset-smoke.mjs
+```
+
+Validates every `presets/*.json` (except samples) via `validateSystemDefinition` + sample derived compute.