Fix ImageEditor brush preview dead area on vertical images

[MaxwellCalkin]

Summary

Fixes #12380

When a new image is loaded into the ImageEditor, the canvas dimensions change but the brush stroke/preview textures are not recreated. This causes a "dead area" where the real-time brush preview doesn't render — the user can draw (the stroke appears on mouse release) but cannot see the preview while drawing.

Root cause

BrushTool.set_tool() only reinitializes brush textures when the draw/erase mode changes or textures are not yet initialized. When an image is loaded and set_tool("draw") is called again (from ImageEditor.reset()), neither condition is true — the mode hasn't changed and textures are already initialized from the initial setup. So the textures keep their old dimensions (from the initial canvas size), and the preview_sprite only covers part of the image.

This is most visible with vertical (portrait) images because the canvas height increases significantly beyond the initial canvas size, leaving a large dead zone at the bottom of the image.

Fix

• In BrushTool.set_tool(), add a dimension check: compare the current image_container.getLocalBounds() against the stored texture dimensions. If they differ, reinitialize the textures.
• Also fix BrushTextures.reinitialize() to use getLocalBounds() instead of image_container.width/height, which includes the container's scale transform and would give incorrect comparisons.

Changes

• js/imageeditor/shared/brush/brush.ts: Add dimensions_changed check in set_tool() to trigger texture reinitialization when canvas dimensions change.
• js/imageeditor/shared/brush/brush-textures.ts: Fix reinitialize() to correctly compare local bounds dimensions instead of scale-affected container dimensions.

Test plan

• Load a vertical (portrait) image into gr.ImageEditor
• Select the brush tool and draw across the entire image
• Verify the real-time brush preview is visible everywhere, including the bottom of the image
• Verify that drawing on horizontal images still works correctly
• Verify that switching between brush and eraser tools works correctly after loading an image
• Verify undo/redo still works correctly

Reproduction script from the issue:

import gradio as gr
def buildImageEditorUI():
    inputImage = gr.Image(elem_classes=["mcww-hidden", "editor-input-image"])
    editor = gr.ImageEditor(type="pil", label="Editor", height="80vh",
        show_download_button=False, elem_classes=["helpers-editor"])
    with gr.Row():
        result = gr.Image(interactive=False, label="Result", height="220px", format="png")
    inputImage.change(
        fn=lambda x: x,
        inputs=[inputImage],
        outputs=[editor],
    )
    editor.change(
        fn=lambda x: x['composite'],
        inputs=[editor],
        outputs=[result],
    )
with gr.Blocks() as demo:
    buildImageEditorUI()
demo.launch()

[iwr-redmond]

cc @pngwn