PHASE 2: Implements balance assertions for reconciliation

Adds balance assertion functionality to enable admins to verify accounting accuracy.

This includes:
- A new `balance_assertions` table in the database
- CRUD operations for balance assertions (create, get, list, check, delete)
- API endpoints for managing balance assertions (admin only)
- UI elements for creating, viewing, and re-checking assertions

Also, reorders the implementation roadmap in the documentation to reflect better the dependencies between phases.

BEANCOUNT_PATTERNS.md

@@ -866,29 +866,29 @@ async def validate_journal_entry(entry: CreateJournalEntry) -> list[CastleError]
 
 ## Implementation Roadmap
 
-### Phase 1: Foundation (High Priority)
+### Phase 1: Foundation (High Priority) ✅ COMPLETE
 1. ✅ Switch from `float` to `Decimal` for fiat amounts
 2. ✅ Add `meta` field to journal entries for audit trail
 3. ✅ Add `flag` field for transaction status
 4. ✅ Implement hierarchical account naming
 
-### Phase 2: Core Logic (Medium Priority)
-5. Create `core/` module with pure accounting logic
-6. Implement `CastleInventory` for position tracking
-7. Move balance calculation to `core/balance.py`
-8. Add comprehensive validation in `core/validation.py`
+### Phase 2: Reconciliation (High Priority) - No dependencies
+5. Implement balance assertions
+6. Add reconciliation API endpoints
+7. Build reconciliation UI
+8. Add automated daily balance checks
 
-### Phase 3: Validation (Medium Priority)
-9. Create plugin system architecture
-10. Implement `check_balanced` plugin
-11. Implement `check_receivables` plugin
-12. Add plugin configuration UI
+### Phase 3: Core Logic Refactoring (Medium Priority) - Improves code quality
+9. Create `core/` module with pure accounting logic
+10. Implement `CastleInventory` for position tracking
+11. Move balance calculation to `core/balance.py`
+12. Add comprehensive validation in `core/validation.py`
 
-### Phase 4: Reconciliation (High Priority)
-13. Implement balance assertions
-14. Add reconciliation API endpoints
-15. Build reconciliation UI
-16. Add automated daily balance checks
+### Phase 4: Validation Plugins (Medium Priority) - Works better after Phase 3
+13. Create plugin system architecture
+14. Implement `check_balanced` plugin
+15. Implement `check_receivables` plugin
+16. Add plugin configuration UI
 
 ### Phase 5: Advanced Features (Low Priority)
 17. Add tags and links to entries