Implement Schedule Tool

**Phase:** 2 - High-Value, Low-Risk
**Priority:** High

**Why:** High value for monitoring, single API.

**Tasks:**
- [ ] Map Service IDs (본회의/위원회 일정)
- [ ] `get_schedule(date_range)`
- [ ] Pydantic models
- [ ] Tests

**Acceptance Criteria:**
- [ ] Returns plenary/committee schedules
- [ ] Supports date filtering (today, week, custom)

**Related to:** #11