[BUG] [Remediation] - Create Task shows 'Failed to create task' error — task creation non-functional (regression update on #625)

## Bug Description
The `Remediation Task` creation flow now shows a red error message **"Failed to create task"** inline in the dialog (improvement over #625 which reported silent close with no feedback). However, the task creation still fails completely — no task is persisted to the database regardless of input.

This affects all systems in the PEO-790 org context. Tested on system `b4d0aca6-cdb1-4630-84ae-df93b2747178`.

## Update from #625
- **IMPROVEMENT**: The dialog now stays open and shows "Failed to create task" error (previously it closed silently with no feedback).
- **STILL FAILING**: No task is actually created. The task count remains 0 after submission.

## Steps to Reproduce
1. Navigate to `/systems/{id}/remediation`
2. Click "Create Task" button
3. Dialog opens with Severity, Control ID, Task Title*, Description, Due Date fields
4. Fill in "Task Title" (required field)
5. Click "Create Task" button (enabled when title is filled)
6. **Result**: Red error banner "Failed to create task" appears in dialog. Task count remains 0.

## Expected Behavior
Task should be created and appear in the remediation table. Dialog should close with success confirmation.

## Actual Behavior
"Failed to create task" error shown inline in the still-open dialog. No task persisted. No detail on why the creation failed (API error, missing field, etc.)

## Console Errors
No JavaScript console errors captured — the failure is silent at the browser level (API error not surfaced).

## Browser/Environment
Azure Container Apps Dashboard v2
Browser: Chromium (Playwright/Hermes browser)
System: b4d0aca6-cdb1-4630-84ae-df93b2747178 (QA Test System 2026-06-25T17:48:00Z)
Date: 2026-07-08
Related: #625

## Playwright Test Code
```typescript
test('[remediation] Create task succeeds and appears in list', async ({ page }) => {
await page.goto('/systems/b4d0aca6-cdb1-4630-84ae-df93b2747178/remediation');
await page.click('button:has-text("Create Task")');
await page.fill('[placeholder="Describe the remediation task"]', 'Test Task AC-2');
await page.click('button:has-text("Create Task"):not([disabled])');
// Should NOT show error
await expect(page.locator('text=Failed to create task')).not.toBeVisible();
// Should show task in list
await expect(page.locator('table')).toContainText('Test Task AC-2');
});
```

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