feat: Bento-style grid layout option for link buttons

[KotaHusky]

Summary

Replace (or offer as an alternative to) the current two-column link button list with a Bento grid layout. Bento-style grids allow links to have varying sizes, icons, preview images, or short descriptions — making the page feel more like a rich personal hub and less like a plain Linktree clone.

Inspiration

• Bento.me popularized the grid-of-blocks layout for personal pages; it was acquired by Linktree in 2024 specifically because this pattern resonates with creators
• The current homepage already has a 2-column grid on sm: breakpoints — extending this to a proper Bento grid is a natural evolution
• Visual differentiation between links (e.g. a larger "Photo Commission" card vs a smaller "Tip" card) helps guide visitors toward the most important actions

Proposed Layout

┌──────────────────────┬───────────┐
│  Photo Commission    │   Tip     │
│  [large card, 2col]  │           │
├───────────┬──────────┴───────────┤
│  Gallery  │  Furtrack            │
│           │                      │
├───────────┴──────────┬───────────┤
│  Barks & Rec         │ Technique │
│                      │  (soon)   │
└──────────────────────┴───────────┘

Each card can optionally carry:

• An icon (emoji or Heroicon)
• A short subtitle (1 line)
• A "coming soon" dimmed state (already used for "Technique (Soon)")

Acceptance Criteria

• BentoGrid component renders a CSS Grid layout with configurable column spans per card
• Card config is data-driven (array of objects in app/config.ts or page.tsx) — not hardcoded JSX for each button
• Cards support span property (1 or 2 columns) to create asymmetric layouts
• "Disabled" / coming-soon cards are visually distinct (dimmed, cursor-not-allowed, no hover effect)
• Layout is responsive: single column on mobile, grid on sm: and above
• Existing HomepageButton tests remain passing (or component is replaced and tests updated)
• Snapshot/visual test for the grid layout