[BUG] [MCP/Assessment] - compliance assessment returns SUBSCRIPTION_NOT_CONFIGURED — no in-product path to resolve

## Bug Description

When running a compliance assessment via `/mcp/chat`, the API returns `SUBSCRIPTION_NOT_CONFIGURED` error with no tools executed. The error message instructs users to "set my subscription to " but there is no documented way to do this from the SPIN Agent interface.

This blocks the compliance assessment workflow entirely for users who have not pre-configured a subscription ID.

## Steps to Reproduce

```bash
BASE="https://ca-ato-copilot-mcp-v2.blackwater-9393aa1a.centralus.azurecontainerapps.io"
SYSTEM_ID="92afdc15-bc6f-4648-8073-ad6af396cf97"

curl -s --max-time 30 -X POST -H 'Content-Type: application/json' \
-d "{\"message\":\"Run compliance assessment for Coastal Watch control AC-2\",\"systemId\":\"$SYSTEM_ID\"}" \
"$BASE/mcp/chat"
```

## Expected Behavior

The compliance assessment should run and return assessment results, or at minimum prompt the user for subscription selection via the SPIN Agent interface.

## Actual Behavior

```json
{
"success": true,
"response": "⚠️ No subscription configured. Use 'set my subscription to ' first.\nError: SUBSCRIPTION_NOT_CONFIGURED",
"toolsExecuted": [],
"errors": []
}
```

Zero tools are executed. No UI path is surfaced in the chat to configure a subscription. Users are left with no actionable path forward.

## Impact

- Blocks "Run compliance assessment" user flow
- Blocks "Assess" RMF phase progression
- No in-product guidance on how to resolve

## Browser/Environment

MCP API v2: https://ca-ato-copilot-mcp-v2.blackwater-9393aa1a.centralus.azurecontainerapps.io
Date: 2026-06-30T20:40:00Z
Sweep: Automated 4-hour QA sweep

## Playwright Test Code

```typescript
test('compliance assessment should not require external subscription config', async ({ page }) => {
const response = await fetch(`${MCP_BASE}/mcp/chat`, {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({
message: 'Run compliance assessment for control AC-2',
systemId: COASTAL_WATCH_SYSTEM_ID
})
});
const data = await response.json();
expect(data.response).not.toContain('SUBSCRIPTION_NOT_CONFIGURED');
expect(data.toolsExecuted.length).toBeGreaterThan(0);
});
```

*Filed by Oracle — Automated 4-hour QA Sweep 2026-06-30T20:40:00Z*