fix(widgets): restore Preact as JSX renderer, align with @deck.gl/widgets design

[charlieforward9]

Summary

Reverts the preact removal from #532 and restores Preact as the internal JSX renderer for @deck.gl-community/widgets, aligning with the design intent established by @deck.gl/widgets (all official widgets use render() from Preact internally).

The original motivation for removing Preact was a Vite source-alias build failure when consuming widget source directly. The correct fix is per-file /** @jsxImportSource preact */ pragmas — not removing Preact.

Changes

• Revert refactor: remove preact dependency from widgets module #532 — restore .tsx files with Preact JSX, jsxImportSource: "preact" tsconfig, VNode return types on renderObject()/renderCluster()
• Add /** @jsxImportSource preact */ pragma to all .tsx widget files — overrides jsxImportSource per-file so TypeScript uses Preact's JSX factory even when compiled under a React project's tsconfig (the common case for Vite source aliases)
• Remove redundant deck?: Deck | null redeclarations from HtmlOverlayWidget, PanWidget, ZoomRangeWidget — base Widget class already declares deck?: Deck<ViewsT>, and the | null conflicted with the base type (Deck | undefined)
• this.deck = null → undefined in onRemove() to match base class type
• Widen hasViewManager() parameter to Deck | null | undefined to match callers

Why Preact, not vanilla DOM

@deck.gl/widgets uses Preact internally for all built-in widgets (ZoomWidget, FullscreenWidget, CompassWidget, GimbalWidget). The UI Module RFC explicitly chose Preact for its component model at minimal bundle size (~3kb). Community widgets should follow the same pattern — VanillaJS public interface, Preact internally.

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