Reserve health: add projected cash flow with special assessments; add Last Updated to cards

Reserve fund analysis now includes 12-month forward projection with
special assessment income (by frequency), monthly budget data,
capital project costs, and investment maturities. AI prompt updated
to evaluate projected reserve liquidity and timing risks.

Both health score dashboard cards now show a subtle "Last updated"
timestamp at the bottom.

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

frontend/src/pages/dashboard/DashboardPage.tsx

@@ -214,6 +214,11 @@ function HealthScoreCard({ score, title, icon }: { score: HealthScore | null; ti
           </Group>
         </Stack>
       </Group>
+      {score.calculated_at && (
+        <Text size="10px" c="dimmed" ta="right" mt={6} style={{ opacity: 0.7 }}>
+          Last updated {new Date(score.calculated_at).toLocaleDateString()} at {new Date(score.calculated_at).toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' })}
+        </Text>
+      )}
     </Card>
   );
 }