Fix bugs: monthly actuals month filter, unit assessments, project funding logic, UI cleanup

- Fix monthly actuals showing same data for all months (SQL JOIN excluded
  month filter from SUM — added je.id IS NOT NULL guard)
- Fix units displaying $0 assessment by reading from assessment group
  instead of stale unit field; add special assessment column
- Replace proportional project funding with priority-based sequential
  allocation — near-term items get fully funded first; add is_funding_locked
  flag so users can manually lock a project's fund balance
- Remove post-creation opening balance UI (keep only initial balance on
  account creation); remove redundant Fund filter dropdown from Accounts

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

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

@@ -311,6 +311,7 @@ export class TenantSchemaService {
         account_id UUID REFERENCES "${s}".accounts(id),
         notes TEXT,
         is_active BOOLEAN DEFAULT TRUE,
+        is_funding_locked BOOLEAN DEFAULT FALSE,
         created_at TIMESTAMPTZ DEFAULT NOW(),
         updated_at TIMESTAMPTZ DEFAULT NOW()
       )`,