feat: Add story points, due dates, priority levels, and task categories to Kanban cards

[Dhruv-0-Arora]

Summary

This PR introduces several new card-level features to the Obsidian Kanban plugin, bringing it closer to full-featured project management tools like Jira while maintaining the simplicity of markdown-backed storage.

New Features

1. Story Points

• Each card now displays a story point input field in the bottom-right corner.
• Accepts any number (designed for Fibonacci values: 1, 2, 3, 5, 8, 13…).
• Defaults to 0 when no value is assigned.
• Stored in markdown as sp{value}.

2. Due Date Bubble

• A date bubble is shown in the bottom-left corner of each card.
• Clicking the bubble opens a calendar picker for selecting a due date.
• Displays the number of days remaining until the due date (e.g., "3d").
• Leverages the existing @{date} markdown syntax under the hood.

3. Priority Levels

• Cards can be assigned Low, Medium, or High priority via a drop-up selector next to the story points field.
• Visual indicators on the card:
  • High priority — red border + box-shadow.
  • Medium priority — yellow border + box-shadow.
  • Low / None — default card appearance.
• Stored in markdown as !!{high}, !!{medium}, or !!{low}.
• The dropdown is portaled to document.body so it is never clipped by card overflow.

4. Task Categories

• Users can define custom categories (e.g., per class, project, or topic) with a name and color through a dedicated modal.
• The modal is accessible via a tag icon button in the Kanban header (next to "Add a list").
• Categories can be reordered using up/down arrows in the modal.
• Each card has a category selector (bottom-left, next to the date bubble) that shows:
  • A colored dot matching the assigned category.
  • The category name as a text label.
• Cards with an assigned category display a full-height colored stripe on the left edge of the card, matching the category color.
• Stored in markdown as cat{CategoryName}.

5. Click-off to Confirm Edit

• Previously, the only way to stop editing a card was pressing Enter.
• Cards now confirm and exit editing when clicking anywhere outside the card.

Technical Details

• All new metadata (story points, priority, category) uses the existing genericWrappedExtension markdown parsing pattern, keeping the data fully portable in plain markdown.
• New Preact components: StoryPoints.tsx, DateBubble.tsx, PrioritySelect.tsx, CategorySelect.tsx, CategoryModal.tsx.
• Dropdowns for priority and category use createPortal to render into document.body, avoiding CSS overflow, contain, and will-change clipping issues.
• Category settings are stored in the board's YAML/JSON settings block alongside other board-level configuration.

Screenshots

Test Plan

• Create a new Kanban board and verify default card layout (story points at 0, empty date bubble, no priority, no category)
• Assign story points and verify they persist after reload
• Select a due date via the calendar picker and verify the "days until" count is correct
• Set priority to High/Medium/Low and verify the border color changes accordingly
• Open the category modal, create categories with distinct colors, and reorder them
• Assign categories to cards and verify the left-side colored stripe and label appear
• Change a card's category and verify the stripe color updates
• Remove a category assignment and verify the stripe disappears
• Verify clicking outside an edited card confirms the edit
• Verify all features work correctly across multiple columns
• Verify the priority and category dropdowns position correctly regardless of scroll position or column