fix: enforce read-only restrictions for viewer role across 5 pages

Audit and fix viewer (read-only) user permissions:
- Dashboard: hide health score refresh buttons
- Accounts: hide investment edit icons
- Invoices: hide Apply Late Fees and Generate Invoices buttons
- Capital Planning: disable drag-and-drop, hide grip handles and edit buttons
- Investment Planning: hide AI Recommendations refresh button

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

frontend/src/pages/investment-planning/InvestmentPlanningPage.tsx

@@ -36,6 +36,7 @@ import {
 import { useQuery } from '@tanstack/react-query';
 import { notifications } from '@mantine/notifications';
 import api from '../../services/api';
+import { useIsReadOnly } from '../../stores/authStore';
 
 // ── Types ──
 
@@ -347,6 +348,7 @@ function RecommendationsDisplay({
 export function InvestmentPlanningPage() {
   const [ratesExpanded, setRatesExpanded] = useState(true);
   const [isTriggering, setIsTriggering] = useState(false);
+  const isReadOnly = useIsReadOnly();
 
   // Load financial snapshot on mount
   const { data: snapshot, isLoading: snapshotLoading } = useQuery<FinancialSnapshot>({
@@ -696,15 +698,17 @@ export function InvestmentPlanningPage() {
               </Text>
             </div>
           </Group>
-          <Button
-            leftSection={<IconSparkles size={16} />}
-            onClick={handleTriggerAI}
-            loading={isProcessing}
-            variant="gradient"
-            gradient={{ from: 'grape', to: 'violet' }}
-          >
-            {aiResult ? 'Refresh Recommendations' : 'Get AI Recommendations'}
-          </Button>
+          {!isReadOnly && (
+            <Button
+              leftSection={<IconSparkles size={16} />}
+              onClick={handleTriggerAI}
+              loading={isProcessing}
+              variant="gradient"
+              gradient={{ from: 'grape', to: 'violet' }}
+            >
+              {aiResult ? 'Refresh Recommendations' : 'Get AI Recommendations'}
+            </Button>
+          )}
         </Group>
 
         {/* Processing State */}