#637 Time-based capacity variations for rate limiting

Currently the schedule system only supports on/off (allowed/blocked) time windows. Need to support variable rate limits based on time of day. **Use Case:** - Business hours (9-17): 100 emails/hour - Evening (17-23): 10 emails/hour - Night (23-08): 2 emails/hour or blocked **Current State:** - schedule_report has 'capacity' field in windows but it's not used - ToolRateLimiter uses static limits from config (requests_per_minute/hour/day) **Required Changes:** 1. Enhance _check_schedule() to extract capacity from current window 2. Use window capacity to override static limits when present 3. Update schedule_checker to populate capacity in windows based on TJP **Data Model (already exists):** ```json { "windows": [ { "start": "2025-12-22T09:00:00Z", "end": "2025-12-22T17:00:00Z", "capacity": {"per_hour": 100, "per_day": 500} } ] } ``` **Related:** Issue #635 (Tool Rate Limiting with ScriptPlan)