Implement Card Resize + Scroll Rework

[PauloMFJ]

Overview

Cards can now be manually resized on the canvas, and their content scrolls internally under a pinned title instead of resizing the whole card.

Changes

• Manual card resizing — Enabled tldraw resizing on the card shape (onResize via resizeBox) with a CARD_SIZE_MIN of 300×220. Added an isManuallyResized prop that, once set, tells useCardAutoHeight to stop syncing height so the user's chosen size sticks.
• Cursor-only resize UI — Reworked the selection foreground overlay to keep hit-testing/resize-cursors active while rendering no handles or selection frame.
• New Card.Content component — A titled scroll region that fills the card: the title/header is pinned to the top and the body scrolls beneath it, with a divider that appears on scroll (data-has-scrolled). Wheel-capture logic moved here so cards scroll from anywhere over the card, not just the scroll area.
• Auto-height rework — useCardAutoHeight now measures container + content refs (accounting for fixed chrome like title/padding) instead of scrollHeight.
• Responsive charts — Line chart now uses recharts ResponsiveContainer (width fills the resizable card; height stays fixed), dropping the hardcoded CHART_WIDTH.
• Config rename — CARD_VARIANT_MAX → CARD_VARIANT_SIZE_DEFAULT to reflect that it's now a default (resizable) footprint rather than a hard max; updated all references.
• Base card cleanup — CardBase now takes a childrenContainerRef prop; removed auto-height/scroll wiring from it.
• Text card styles — Migrated markdown spacing to :not(:first-child) top-margins. Ensures that we don't add margin bottom or top on first / last elements.

Screenshots:

New card with scroll:

[gemini-code-assist]

Code Review

This pull request introduces manual resizing capabilities for cards on the canvas. It refactors the card components to use a new CardContent component that manages a titled scroll region, and updates useCardAutoHeight to stop auto-syncing height once a card is manually resized. The review feedback identifies a critical bug where the ResizeObserver in useCardAutoHeight observes the outer container instead of the inner content. Because the container now has a fixed height, the observer will fail to trigger when the content size changes, breaking the auto-height functionality.