[WM-IMP-8] ConMon scheduling model missing — continuous monitoring cadence not implementable

## WM-IMP-8 — ConMon Scheduling Model Missing

**Category:** Improvement | **Priority:** Medium

### Observation
The ConMon module has no scheduling model. Assessment frequencies cannot be configured or tracked. (Related to WM-BW-8 which addresses the regulatory gap; this improvement addresses the scheduling architecture.)

### Recommendation
Implement a ConMon scheduling model that supports per-control-family frequencies and generates upcoming assessment tasks.

### Acceptance Criteria
- [ ] Scheduling model supports: continuous, monthly, quarterly, semi-annual, annual frequencies
- [ ] Per-control-family and per-tier scheduling supported
- [ ] Upcoming assessments appear in a schedule/calendar view
- [ ] Overdue assessments flagged and surfaced in dashboard