feat: add Board Planning module with investment/assessment scenario modeling

Implements Phase 11 Forecasting Tools - a "what-if" scenario planning system
for HOA boards to model financial decisions before committing.

Backend:
- 3 new tenant-scoped tables: board_scenarios, scenario_investments, scenario_assessments
- Migration script (013) for existing tenants
- Full CRUD service for scenarios, investments, and assessments
- Projection engine adapted from cash flow forecast with investment/assessment deltas
- Scenario comparison endpoint (up to 4 scenarios)
- Investment execution flow: converts planned → real investment_accounts + journal entry

Frontend:
- New "Board Planning" sidebar section with 3 pages
- Investment Scenarios: list, create, detail with investments table + timeline
- Assessment Scenarios: list, create, detail with changes table
- Scenario Comparison: multi-select overlay chart + summary metrics
- Shared components: ProjectionChart, InvestmentTimeline, ScenarioCard, forms
- AI Recommendation → Investment Plan integration (Story 1A)

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

frontend/src/pages/board-planning/components/ScenarioCard.tsx

@@ -0,0 +1,74 @@
+import { Card, Group, Text, Badge, ActionIcon, Menu } from '@mantine/core';
+import { IconDots, IconTrash, IconEdit, IconPlayerPlay } from '@tabler/icons-react';
+
+const fmt = (v: number) => v.toLocaleString('en-US', { style: 'currency', currency: 'USD', maximumFractionDigits: 0 });
+
+const statusColors: Record<string, string> = {
+  draft: 'gray',
+  active: 'blue',
+  approved: 'green',
+  archived: 'red',
+};
+
+interface Props {
+  scenario: any;
+  onClick: () => void;
+  onEdit: () => void;
+  onDelete: () => void;
+}
+
+export function ScenarioCard({ scenario, onClick, onEdit, onDelete }: Props) {
+  return (
+    <Card withBorder p="lg" style={{ cursor: 'pointer' }} onClick={onClick}>
+      <Group justify="space-between" mb="xs">
+        <Group gap="xs">
+          <Text fw={600}>{scenario.name}</Text>
+          <Badge size="xs" color={statusColors[scenario.status] || 'gray'}>
+            {scenario.status}
+          </Badge>
+        </Group>
+        <Menu withinPortal position="bottom-end" shadow="sm">
+          <Menu.Target>
+            <ActionIcon variant="subtle" color="gray" onClick={(e: any) => e.stopPropagation()}>
+              <IconDots size={16} />
+            </ActionIcon>
+          </Menu.Target>
+          <Menu.Dropdown>
+            <Menu.Item leftSection={<IconEdit size={14} />} onClick={(e: any) => { e.stopPropagation(); onEdit(); }}>
+              Edit
+            </Menu.Item>
+            <Menu.Item leftSection={<IconTrash size={14} />} color="red" onClick={(e: any) => { e.stopPropagation(); onDelete(); }}>
+              Archive
+            </Menu.Item>
+          </Menu.Dropdown>
+        </Menu>
+      </Group>
+      {scenario.description && (
+        <Text size="sm" c="dimmed" mb="sm" lineClamp={2}>{scenario.description}</Text>
+      )}
+      <Group gap="lg">
+        {scenario.scenario_type === 'investment' && (
+          <>
+            <div>
+              <Text size="xs" c="dimmed">Investments</Text>
+              <Text fw={600}>{scenario.investment_count || 0}</Text>
+            </div>
+            <div>
+              <Text size="xs" c="dimmed">Total Principal</Text>
+              <Text fw={600} ff="monospace">{fmt(parseFloat(scenario.total_principal) || 0)}</Text>
+            </div>
+          </>
+        )}
+        {scenario.scenario_type === 'assessment' && (
+          <div>
+            <Text size="xs" c="dimmed">Changes</Text>
+            <Text fw={600}>{scenario.assessment_count || 0}</Text>
+          </div>
+        )}
+      </Group>
+      <Text size="xs" c="dimmed" mt="sm">
+        Updated {new Date(scenario.updated_at).toLocaleDateString()}
+      </Text>
+    </Card>
+  );
+}