Introduce a dedicated Zustand ArtifactSlice to manage artifact selection
state with mutual exclusion against the main file tree. Artifact files
from the sandbox can now be opened as tabs in the skill editor, rendered
via a lightweight ArtifactContentPanel that reuses ReadOnlyFilePreview.
- Add guards in tool-block component to skip metadata read/write when Start tab is active
- Add guard in tool-picker-block to prevent writing tool config to Start tab
- Add guard in use-sync-tree-with-active-tab to skip tree sync for Start tab
Replace getAncestorIds(treeData) with node.parent chain traversal
for more efficient ancestor lookup. This avoids re-traversing the
tree data structure and uses react-arborist's built-in parent refs.
Also rename hook to useSyncTreeWithActiveTab for clarity.
