Bug & tweak sprint: fix financial calculations, add quarterly report, enhance dashboard

- Fix Accounts page: include investment accounts in Est. Monthly Interest calc,
  add Fund column to investment table, split summary cards into Operating/Reserve
- Fix Cash Flow: ending balance now respects includeInvestments toggle
- Fix Budget Manager: separate operating/reserve income in summary cards
- Fix Projects: default sort by planned_date instead of name
- Add Vendors: last_negotiated date field with migration, CSV import/export
- New Quarterly Financial Report: budget vs actuals, over-budget flagging, YTD
- Enhance Dashboard: separate Operating/Reserve fund cards, expanded Quick Stats
  with monthly interest, YTD interest earned, planned capital spend

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

backend/src/database/tenant-schema.service.ts

@@ -202,6 +202,7 @@ export class TenantSchemaService {
         default_account_id UUID REFERENCES "${s}".accounts(id),
         is_active BOOLEAN DEFAULT TRUE,
         ytd_payments DECIMAL(15,2) DEFAULT 0.00,
+        last_negotiated DATE,
         created_at TIMESTAMPTZ DEFAULT NOW(),
         updated_at TIMESTAMPTZ DEFAULT NOW()
       )`,