Bug: Raw submissions table only shows columns from first submission (missing fields)

## Bug: Raw submissions table only shows columns from first submission (missing fields)

**File:** `src/pages/TemplateDetailAnalytics.jsx:125-127`

### Problem
The raw submissions table builds its column headers from only the first submission's data:
```js
const allSubmissionKeys = submissions.length > 0
  ? Object.keys(submissions[0].submittedData || {})
  : [];
```

If later submissions have additional fields (e.g., optional fields that only some users fill), those columns won't appear. Conversely, if the first submission is missing a field that later submissions have, that data is invisible.

### Impact
- Incomplete data display in the submissions table
- Paginated data changes columns on each page (page 1 might have different keys than page 2)

### Fix
Collect all unique keys across all submissions on the current page:
```js
const allSubmissionKeys = submissions.length > 0
  ? [...new Set(submissions.flatMap(s => Object.keys(s.submittedData || {})))]
  : [];
```

Or better: use the template's `enabledFields` from `detail.enabledFields` since that defines the complete schema:
```js
const allSubmissionKeys = detail.enabledFields;
```

### Severity
**Medium** — Data display issue, not a crash. But users may miss seeing fields that don't appear in the first row.

### Phase
Introduced in Phase 2 (PR #27, merged).


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Bug: Raw submissions table only shows columns from first submission (missing fields) #36