feat(reporting): add Finding ID column

ID was already stored in the cache from f.id; exposed as a sortable
column (filterable: false — too many unique values to be useful as a filter).
Existing users get it appended to the end of their saved column order
via the loadColumnOrder merge logic; new users see it first.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/pages/ReportingPage.js

@@ -9,6 +9,7 @@ const STORAGE_KEY = 'steam_findings_columns_v1';
 // Column definitions — source of truth for labels, sort behaviour, rendering
 // ---------------------------------------------------------------------------
 const COLUMN_DEFS = {
+    findingId:   { label: 'Finding ID',  sortable: true,  filterable: false                  },
     severity:    { label: 'Severity',    sortable: true,  filterable: true                   },
     title:       { label: 'Title',       sortable: true,  filterable: true                   },
     cves:        { label: 'CVEs',        sortable: true,  filterable: true,  multiValue: true },
@@ -23,6 +24,7 @@ const COLUMN_DEFS = {
 };
 
 const DEFAULT_COLUMN_ORDER = [
+    { key: 'findingId',   visible: true },
     { key: 'severity',    visible: true },
     { key: 'title',       visible: true },
     { key: 'cves',        visible: true },
@@ -63,6 +65,7 @@ function saveColumnOrder(order) {
 // ---------------------------------------------------------------------------
 function getVal(finding, key) {
     switch (key) {
+        case 'findingId':   return finding.id ?? '';
         case 'severity':    return finding.severity ?? 0;
         case 'title':       return finding.title ?? '';
         case 'hostName':    return finding.hostName ?? '';
@@ -449,6 +452,12 @@ function FilterDropdown({ anchorEl, colKey, findings, activeFilter, onFilterChan
 // ---------------------------------------------------------------------------
 function TableCell({ colKey, finding }) {
     switch (colKey) {
+        case 'findingId':
+            return (
+                <td style={{ padding: '0.45rem 0.75rem', whiteSpace: 'nowrap', color: '#475569', fontFamily: 'monospace', fontSize: '0.68rem' }}>
+                    {finding.id || '—'}
+                </td>
+            );
         case 'severity': {
             const sc = severityColor(finding.vrrGroup);
             return (