feat(data-weaver): Remove fitCardSize; use default card widths

[pablonoel]

Overview

Card widths to use variant sizes when rendering.

Changes Made

Delete the fitCardSize function and stop capping card widths to the grid column width. atlas_provider now uses CARD_VARIANT_SIZE_DEFAULT directly when placing cards, and register_card_placement no longer imports CARD_SIZE_MIN or implements fitCardSize.

PLACEMENT.md updated to reflect that cards use their default widths and rows may run wider than the viewport.

Testing Done

Describe the steps you took to test these changes (please also list commands ran if possible).

• Unit tests passed
• Integration tests passed
• Manual verification

Checklist

• I have followed the style guidelines of this project.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings.

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[gemini-code-assist]

Code Review

This pull request removes the fitCardSize utility and its usage, meaning cards will now always use their default width (CARD_VARIANT_SIZE_DEFAULT) instead of being capped to the grid's column width. The documentation in PLACEMENT.md has been updated to reflect this change. Feedback is provided regarding a potential issue where an invalid or missing content.variant could result in an undefined size, potentially corrupting the canvas state; a defensive guard is suggested to prevent this.