[BUG] [Assessments] - Generate SAP modal now appears (partial fix #624) but blocked by baseline gate — no navigation path to set baseline

## Bug Description
The "Generate SAP" button on the Assessments page previously showed "no feedback" (issue #624). In this sweep, the button NOW correctly opens a confirmation modal — this is a partial fix.

However, clicking "Generate SAP" within the modal now reveals a new error:

> **"No control baseline found for system '{system_id}'. Select a baseline before generating a SAP."**

The modal shows the system name and impact level (`—`), confirming the system is found, but the SAP cannot proceed because no control baseline has been selected/assigned via categorization.

**This is a different failure mode from #551** (which referenced the error appearing in the page body, not in a modal). The modal is new behavior — so the regression from #624 appears RESOLVED, but the baseline gate (#551) remains blocked.

## Key Changes from Prior Sweep
- **FIXED** (#624): Generate SAP button now opens a confirmation modal with system info. No longer a silent dead button.
- **STILL FAILING** (#551): SAP generation blocked by "No control baseline found" error. The error now surfaces within the new modal (improvement in UX).

## Steps to Reproduce
1. Navigate to `/systems/{id}/assessments`
2. Click "Generate SAP" button
3. Modal opens with system info and Generate SAP button
4. Click "Generate SAP" in the modal
5. Error appears: "No control baseline found for system '{id}'. Select a baseline before generating a SAP."

## Expected Behavior
SAP generation should either:
a) Succeed with a default baseline, OR
b) Provide a direct "Set baseline →" link/button in the error that navigates to Categorization

## Actual Behavior
Error shown inline in modal. No navigation path to fix the baseline. Modal remains open showing the error. User must dismiss and find Categorization page manually.

## Related Issues
- #624: Generate SAP had no modal (NOW FIXED — modal appears)
- #551: Generate SAP shows 'No control baseline found' (STILL FAILING — same underlying issue, now shown in modal)

## Browser/Environment
Azure Container Apps Dashboard v2
Browser: Chromium (Playwright/Hermes browser)
System tested: b4d0aca6-cdb1-4630-84ae-df93b2747178
Date: 2026-07-08
Sweep: Automated 4-hour QA sweep

*Filed by Oracle — Automated 4-hour QA Sweep 2026-07-08T23:55:00Z*