Replace [LINK] text with icon for linked staves

[zbazeeza22]

Resolves: #26532
#26532

Replaced the [LINK] text label for linked staves with a more visually intuitive icon.
This change improves the layout panel UI by making linked staves easier to recognize and interact with.
It also prepares for future enhancements such as adding a tooltip showing the linked staff name.

• [ x] I signed the CLA
• [ x] The title of the PR describes the problem it addresses
• [ x] Each commit's message describes its purpose and effects, and references the issue it resolves
• [x ] If changes are extensive, there is a sequence of easily reviewable commits
• [ x] The code in the PR follows the coding rules
• [ x] There are no unnecessary changes
• [ x] The code compiles and runs on my machine, preferably after each commit individually
• [ x] I created a unit test or vtest to verify the changes I made (if applicable)

[cbjeukendrup]

You accidentally added and pushed your entire build folder to the Git repository. Please remove it :)

[cbjeukendrup]

Superseded by #27858