Refactor BaseNodeViewer to use SharedNodeStore for all database operations

[malibio]

Problem

BaseNodeViewer bypasses SharedNodeStore and directly calls database service methods, creating dual persistence paths that cause conflicts and violate single-source-of-truth principle.

Current Architecture (Broken)

BaseNodeViewer → databaseService → database
ReactiveNodeService → SharedNodeStore → tauriNodeService → database

Direct Database Calls in BaseNodeViewer

• databaseService.getNode() - checking node existence
• databaseService.deleteNode() - deleting nodes
• databaseService.updateNode() - updating structural changes
• databaseService.getNodesByOriginId() - loading children
• databaseService.saveNodeWithParent() - saving content (debounced, placeholder-aware)

Issues Caused

1. Duplicate INSERTs - Both paths try to create nodes (temporarily fixed with source.type !== 'viewer' workaround)
2. Conflicting deletes - Not covered by workaround
3. Conflicting structural updates - Not covered by workaround
4. Tests can't catch bugs - Tests use HttpAdapter, real app uses TauriNodeService, SharedNodeStore persistence never tested
5. Inconsistent state - SharedNodeStore.persistedNodeIds tracking doesn't know about BaseNodeViewer's direct saves

Temporary Workaround (Added in #232)

Added && source.type !== 'viewer' check in SharedNodeStore to skip persisting viewer-sourced updates. This prevents duplicate INSERTs but doesn't address all conflicts.

IMPORTANT: This workaround must be removed as part of this refactoring.

Solution

Refactor BaseNodeViewer to use SharedNodeStore for ALL database operations.

Target Architecture

BaseNodeViewer → ReactiveNodeService → SharedNodeStore → tauriNodeService → database

Changes Needed

1. Remove direct database calls from BaseNodeViewer

   • Replace databaseService.getNodesByOriginId() with SharedNodeStore query
   • Replace databaseService.saveNodeWithParent() with sharedNodeStore.updateNode()
   • Replace databaseService.deleteNode() with sharedNodeStore.deleteNode()
   • Replace databaseService.updateNode() with sharedNodeStore.updateNode()

2. Move debouncing to SharedNodeStore

   • Transfer 500ms debounce logic from BaseNodeViewer
   • Make SharedNodeStore placeholder-aware (don't persist empty nodes)
   • Preserve FOREIGN KEY coordination (wait for parent saves before child structural updates)

3. Remove temporary workaround

   • Delete && source.type !== 'viewer' check from SharedNodeStore.updateNode() (line ~284)
   • Delete && source.type !== 'viewer' check from SharedNodeStore.setNode() (line ~367)
   • SharedNodeStore should handle ALL persistence for viewer-sourced updates

4. Update tests

   • SharedNodeStore persistence will now be exercised by integration tests
   • Tests will catch dual persistence bugs automatically

Complexity

• Medium-High
• Requires careful migration of BaseNodeViewer's sophisticated save logic
• Must preserve placeholder handling and FOREIGN KEY coordination
• Need comprehensive testing to ensure no regressions

Related Issues

• Fix Enter Key & Node Creation Operations (17 test failures) #232 - Revealed the dual persistence architecture problem
• Fix Test Environment to Surface Database Errors & Race Conditions #235 - Added test infrastructure to catch database errors

Acceptance Criteria

• All databaseService.* calls removed from BaseNodeViewer
• SharedNodeStore handles all persistence with proper debouncing
• Placeholder nodes not persisted to database
• FOREIGN KEY coordination preserved
• Temporary workaround removed from SharedNodeStore
• All integration tests pass
• Manual testing confirms no regressions