feat(design)!: convert @daffodil/design/image to use signals

[xelaint]

PR Checklist

• Commit message follows our contributing guidelines
• Tests added/updated (for bug fixes/features)
• Documentation added/updated (for bug fixes/features)

PR Type

• Bug fix
• Feature
• Style update
• Refactor
• Test
• Build
• CI
• Docs
• Performance
• Other (please describe)

Current behavior

Part of: #4327

New behavior

Breaking change?

• Yes
• No

BREAKING CHANGE: @daffodil/design/image now exposes the DaffImageComponent inputs src, alt, width, and height as signals rather than plain properties, and renames the load output to loaded.

• Input template bindings ([src], [alt], etc.) continue to work unchanged.
• Programmatic reads must invoke the signal: image.src → image.src(), image.width → image.width(), etc.
• Inputs are now read-only and can no longer be assigned imperatively (image.src = '/image/test.jpg' is no longer supported).

Additional context