fix: zone grid snapping, shelf position panel, deselect on item placement

[wass08]

What does this PR do?

Four small editor fixes:

• Zone tool respects grid snapping — zone drawing snapped to a hardcoded 0.5 step for both cursor move and click; it now reads the editor's gridSnapStep setting (0.5 / 0.25 / 0.1 / 0.05) live, like the wall/column/shelf tools.
• Shelf inspector gets an X/Y/Z position panel — adds a Position group with a vec3 field to shelfParametrics, rendered by the parametric inspector as three X/Y/Z sliders (same renderer the spawn node uses), matching the item panel.
• Item catalog deselects before placement — clicking a catalog item to place it now clears the viewer selection first, so shortcuts (rotate & co) no longer act on both the placement ghost and the previously selected node.
• Level display naming moves to @pascal-app/core — getDefaultLevelName / getLevelDisplayName ("Ground Floor" / "Floor N" / "Basement N") were internal to packages/editor, so viewer-only surfaces couldn't reach them and hand-rolled "Level N" labels instead. Pure domain logic → moved to core and exported from its barrel; the editor package's seven call sites import from there now.

How to test

1. bun dev, open the editor.
2. Zone snap: set the grid snap step to 0.1 in the view toggles, activate the zone tool, and draw — the cursor and committed points should snap at 0.1 m increments (previously always 0.5 m).
3. Shelf panel: place a shelf, select it — the inspector now shows a Position section with X/Y/Z sliders; dragging them moves the shelf.
4. Deselect on placement: select any placed node, then click an item in the catalog and press R while placing — only the ghost rotates, and the previous selection's panel is closed.
5. Level naming: no behavior change inside the editor — level lists still read "Ground Floor / Floor 1 / …". bun run build confirms the import move compiles across core/editor/nodes.

Screenshots / screen recording

N/A — small interactive fixes; behavior is covered by the test steps above.

Checklist

• I've tested this locally with bun dev (verified via typecheck + bun run build; needs a manual pass of the steps above)
• My code follows the existing code style (run bun check to verify)
• I've updated relevant documentation (if applicable)
• This PR targets the main branch

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Project	Status	Preview	Updated (UTC)
pascal	🔴 Failed	–	Jun 10, 2026, 4:41 PM

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