feat(paint): add fill between slice interpolation

[PaulHax]

• Do interpolation
• Reset state on switching images, segment groups, and segment
• Disable painting when in fill between mode

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[PaulHax]

Thoughts on this GUI? @floryst and/or anyone?

[floryst]

How does it compare to Slicer's paint interpolation UX? How will the preview/confirm/cancel functionality work?

[PaulHax]

Here is how Slicer does it:
https://youtu.be/u93kI1MG6Ic?si=YY6uQeepcrtENOW0

1. Preview will run the interpolation code, "stash" the original seg image while swapping in new seg image.
2. Conferm keeps the new image, drops orignal.
3. Cancel drops new, swaps in original.

A video:
https://youtu.be/snA5B1MCgew

[Copilot]

Pull Request Overview

This PR introduces the "Fill Between" feature for painting by adding slice interpolation functionality and updating the paint tool behavior accordingly. Key changes include:

• Adding a new pipeline configuration for morphological contour interpolation in vite.config.ts.
• Introducing a new fillBetween store and updating the PaintMode enum and related logic in the paint tool code.
• Modifying UI components to integrate the new Fill Between mode and its controls.

Reviewed Changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
vite.config.ts	Adds pipeline configuration for morphological contour interpolation.
src/store/tools/paint.ts	Removes the export of ensureActiveSegmentGroupForImage from the paint store.
src/store/tools/fillBetween.ts	Introduces a new store for Fill Between functionality.
src/core/tools/paint/index.ts	Updates PaintMode enum and modifies stroke handling for Fill Between.
src/components/tools/paint/PaintWidget2D.vue	Adds reactive disabling of the widget for Fill Between mode.
src/components/tools/paint/PaintTool.vue	Updates active mode computation to account for Fill Between mode.
src/components/PaintControls.vue	Integrates a new Fill Between button and layout adjustments.
src/components/MiniExpansionPanel.vue	Introduces a reusable expansion panel component.
src/components/FillBetweenControls.vue	Provides controls for previewing, confirming, and canceling fill actions.

Files not reviewed (1)

• package.json: Language not supported

Comments suppressed due to low confidence (2)

src/store/tools/paint.ts:254

• The removal of 'ensureActiveSegmentGroupForImage' from the store's returned API may impact dependent modules; please confirm that all consumers have been updated accordingly.

    ensureActiveSegmentGroupForImage,

src/core/tools/paint/index.ts:80

• The early return for PaintMode.FillBetween bypasses brush value processing; please verify that this behavior is intentional and does not affect other expected fill operations.

if (this.brushValue == null || this.mode === PaintMode.FillBetween) return;