feat(zoom): add trackpad pinch-to-zoom support

[swaroopbutala]

On Mac trackpads, pinch gestures emit wheel events with ctrlKey set to true. This change adds a wheelZoomHandler to DocBaseViewer, ImageBaseViewer, and TextBaseViewer that intercepts these events to provide smooth, proportional zoom behavior without triggering native browser zoom.

Summary of changes:

• DocBaseViewer: Added wheelZoomHandler that adjusts pdfViewer scale proportionally, clamped between MIN_SCALE and MAX_SCALE
• ImageBaseViewer: Added wheelZoomHandler that adjusts image element width proportionally and emits zoom events
• TextBaseViewer: Added wheelZoomHandler that adjusts font size proportionally, plus new bindDOMListeners/unbindDOMListeners lifecycle methods and proper cleanup in destroy()
• All viewers register the wheel listener with { passive: false } to allow preventDefault() and block native browser zoom
• Added comprehensive unit tests for all three viewers

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