feat: add image resizing functionality and styles for image tool

[Famousmaster206]

Description

Resolves #336

Adds Google-Docs-style image resizing to the article editor. Images previously had no way to control their displayed size beyond the existing boolean "stretched" (full-width) toggle, which made it hard to get consistent, accurate image sizing across an article.

This PR:

• Adds a width field (percentage, 15–100%) to the custom Editor.js image block's data model.
• Adds a draggable resize handle to the bottom-right corner of the image in the editor (mouse drag or arrow keys), with aspect ratio locked and width clamped to 15–100% of the content column.
• Setting a custom width automatically disables the existing "stretched" toggle, since the two are mutually exclusive ways of controlling width.
• Persists width through save() and restores it when a saved article is reopened for editing.
• Renders the saved width as an inline style on the <img> in both public-facing renderers (Renderer.tsx and the SSR editorjs-render.ts), so resized images display consistently on published articles.
• Adds editor-only CSS so the handle is visually hidden until hover/focus and has no effect on the public article view.

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

How Has This Been Tested? How can the reviewer test it?

The article editor lives behind an authenticated /admin route gated on Firestore user roles, so it couldn't be exercised directly in this environment. Instead, the resize handle's logic was verified against the real @editorjs/image package in an isolated Playwright harness (same UMD bundle from node_modules, same handle-mounting code):

• Dragging the handle shrinks the image and updates the container width live.
• Releasing the drag persists the final width percentage into the block's data.
• Dragging past the minimum clamps to 15%.
• Dragging past the maximum snaps back to full width (width cleared, "stretched" behavior).

This process caught and fixed a real bug: the handle was initially positioned outside the image container's bounds (right: -6px), which .image-tool__image's overflow: hidden clips — making it invisible/unclickable. It was repositioned inside the container (right: 4px; bottom: 4px) and re-verified.

Also ran tsc --noEmit and eslint on all touched files — no new errors or warnings introduced.

Reviewer testing steps:

1. Open an article in the admin article editor and insert/select an image block.
2. Hover the image to reveal the resize handle at its bottom-right corner; drag it to resize, or focus it and use arrow keys.
3. Save the article and view it on the public article page — the image should render at the chosen width.
4. Toggle "stretched" after setting a custom width (or vice versa) to confirm the two don't conflict.

Checklist

• I have performed a self-review of my own code