feat(mapgen-studio): disable canvas controller and grab cursor pre-run

[mateicanavra]

Before a run completes, the map canvas displayed a grab cursor even though dragging moved nothing visible — the deck controller was active but the only pre-run texture is a CSS graticule behind the canvas, not a deck layer. This gave users a misleading affordance.

DeckCanvas now accepts an interactive prop (defaults to true) that gates both the deck controller and the cursor. When false, the controller is disabled and the cursor is default; when true, the controller (including the moveSpeed: 150 keyboard tuning) and the grab/grabbing cursor are active. Transitions between states apply via setProps so the Deck instance is never remounted.

CanvasStage passes interactive={hasManifest}, using the same boolean gate that controls the "Awaiting matter" overlay, so the cursor and camera interactivity become live exactly when there is rendered matter to interact with.

[github-actions]

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Debug: {"isClosed":false,"isFork":false,"suppress":false,"force":false,"isTopOfStack":false,"hasToken":true,"draft":false}

[mateicanavra]

Merge activity

• Jun 12, 8:50 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jun 12, 10:01 PM UTC: Graphite rebased this pull request as part of a merge.
• Jun 12, 10:01 PM UTC: @mateicanavra merged this pull request with Graphite.