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/modules/units/units.service.ts

@@ -10,6 +10,7 @@ export class UnitsService {
       SELECT u.*,
         ag.name as assessment_group_name,
         ag.regular_assessment as group_regular_assessment,
+        ag.special_assessment as group_special_assessment,
         ag.frequency as group_frequency,
         COALESCE((
           SELECT SUM(i.amount - i.amount_paid)