fix: make unknown tab commands no-ops

[ddebowczyk]

Summary

• resolve tiled and floating tabs by ID before selecting or removing them
• reject unknown tab IDs without changing state or selection
• use the stored tab position when repairing selection after removal
• preserve same-reference no-op behavior for rejected commands

Validation

• npm test -- --run tests/reducer.test.ts
• NODE_OPTIONS=--localstorage-file=/tmp/react-layman-pr01-localstorage.json npm test
• npx --no-install tsc --noEmit
• npm run lint
• npm run build:lib

Known baseline issue

Plain npm test on the current Node runtime still fails only in the existing localStorage test setup. The dedicated portability repair is planned as PR 04; this branch does not change persistence behavior.