[WM-BW-2] RMF Prepare phase has no completion gate or checklist (SP 800-37 Tasks P-1 through P-19)

## WM-BW-2 — RMF Prepare Phase Missing Completion Gate and Task Coverage

**Category:** Broken ATO/RMF Workflow | **Priority:** Critical
**Regulation:** SP 800-37 Rev2 Tasks P-1 – P-19

### Observation
`RmfStep` enum has `Prepare` as the default step. The knowledge service JSON contains only 6 step records (Steps 1–6), so the Prepare step has no knowledge backing. No completion criteria exist. Every system defaults to `CurrentRmfStep=Prepare` with no path forward.

### Evidence
- `RmfStep` enum default observed as `Prepare`
- Knowledge service JSON: only 6 records, none covering Prepare tasks
- No P-1 through P-19 checklist or documented output requirements found

### Impact
All systems are permanently stuck in Prepare. No system can progress to Categorize without manual workarounds. The entire RMF workflow is effectively non-functional from the first step.

### Acceptance Criteria
- [ ] Prepare phase tasks P-1 through P-19 modeled with documented output requirements
- [ ] Completion gate enforced: all required Prepare outputs must be present before system can advance to Categorize
- [ ] Knowledge service updated with Prepare task content
- [ ] UI surfaces Prepare checklist with per-task completion tracking