style(visualization): satisfy biome lint rules

- Add block braces to single-line if/else statements (useBlockStatements).
- Drop two unused imports (setIsLoadingFile, setIsLoadingMap) in
  loadInitialFile.service.ts that became unused when those keys were
  removed from the saved-state restore switch.
- Use const instead of let for an unreassigned variable in codeMapHelper.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>