[M7-T03] Configure Monaco themes

## Task: M7-T03

**Milestone:** M7 - Theming (0.5 day)
**Feature:** RuleZ UI

## Description

Create custom Monaco editor themes for dark and light modes.

## Acceptance Criteria

- [ ] Create `src/styles/monaco-theme.ts`
- [ ] Define light theme
- [ ] Define dark theme
- [ ] Switch theme with app theme

## Dependencies

- Depends on: M2-T01, M7-T01