First shot at a rules file (#119)

Co-authored-by: ellipsis-dev[bot] <65095814+ellipsis-dev[bot]@users.noreply.github.com>

.roo/rules/rules.md

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+# Roo Code Cloud - Development Guidelines
+
+## Testing & Formatting
+
+- **Test**: `pnpm test` (runs all tests via Turbo)
+- **Test single file**: `pnpm test path/to/file.test.ts`
+- **Lint**: `pnpm lint` (ESLint with TypeScript support)
+- **Type check**: `pnpm check-types`
+- **Format**: Files are auto-formatted on commit via lint-staged
+
+## Database & Migrations
+
+- **Push schema**: `pnpm db:push` (applies schema directly, no migration files)
+- **Generate migration**: `pnpm --filter @roo-code-cloud/db db:generate`
+- **Run migrations**: `pnpm --filter @roo-code-cloud/db db:migrate`
+- **Reset DB**: `pnpm db:reset` (drops all data and recreates)
+- **Schema location**: `packages/db/src/schema.ts`
+- **Migration files**: `packages/db/drizzle/*.sql`
+
+## Code Style
+
+- **TypeScript**: Strict mode enabled, use explicit types
+- **Imports**: Use absolute imports with `@/` for src directory
+- **Async/Await**: Prefer over promises, use try-catch for error handling
+- **Naming**: camelCase for variables/functions, PascalCase for types/components
+- **Comments**: Use JSDoc for public APIs, inline comments for complex logic
+- **Error Handling**: Return discriminated unions `{ success: true; data: T } | { success: false; error: string }` for actions
+- **Database**: Use Drizzle ORM with type-safe queries
+- **Testing**: Vitest with globals, mock external dependencies
+- **React**: Functional components with hooks, server components by default
+- **Formatting**: Prettier with default settings (via lint-staged)