widget: add Disableable support to Hyperlink

[AmeeteSh-A]

Description:

This PR adds Disableable support to widget.Hyperlink as discussed in the issue. It implements the standard fyne.Disableable interface (Disable(), Enable(), and Disabled()).

When disabled:

• The hyperlink text and underline render in theme.DisabledColor() instead of the primary color.
• The cursor remains the default pointer on hover.
• Click and Spacebar events are ignored.

Fixes #6455

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

Where applicable:

• Public APIs match existing style and have Since: line.

[dweymouth]

I briefly looked into implementing this myself, but realized it would be complicated as the disable state needs to be propagated to the "sibling" hyperlinks (ie when a HyperlinkSegment wraps in RichText so it is rendered by multiple actual Hyperlinks that are linked together). This PR will have to address that as well to be mergeable.

[AmeeteSh-A]

I briefly looked into implementing this myself, but realized it would be complicated as the disable state needs to be propagated to the "sibling" hyperlinks (ie when a HyperlinkSegment wraps in RichText so it is rendered by multiple actual Hyperlinks that are linked together). This PR will have to address that as well to be mergeable.

I've added a setDisabled helper that properly propagates the disabled state (and clears hover/focus) across all sibling hyperlinks when wrapped.

[andydotxyz]

Why does this comment mention siblings and recursion? A setter does not normally recurse or notify other areas, so why would that be expected in this setter?

[andydotxyz]

Just adding a note here, it looks like AI comments talking about changes that are no longer relevant in the final PR