feat: US-002 — SQLite + Drizzle ORM schema and migrations

- Install better-sqlite3 + drizzle-orm as runtime deps; drizzle-kit + @types/better-sqlite3 as devDeps
- Define 5 tables in src/main/db/schema.ts: clients, projects, tasks, checkpoints, notes
- All IDs are TEXT (UUID); types inferred via InferSelectModel/InferInsertModel
- initDb() in src/main/db/index.ts opens adiuva.db at app.getPath('userData'), runs CREATE TABLE IF NOT EXISTS (non-destructive push), enables WAL mode
- Call initDb() in main process app ready handler
- Externalize better-sqlite3 in vite.main.config.mts; add AutoUnpackNativesPlugin to forge.config.ts
- Add drizzle.config.ts for drizzle-kit CLI support

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

drizzle.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from 'drizzle-kit';
+
+export default defineConfig({
+  schema: './src/main/db/schema.ts',
+  out: './src/main/db/migrations',
+  dialect: 'sqlite',
+});