fix(ui5-shellbar): acc findings fixed

[PetyaMarkovaBogdanova]

5) ShellBar

• Dialog section without computable accessible name: fixed by adding accessibleName to the overflow popover.

Component	Issue	Not by spec	Good to have	Spec refs	Spec quote sentence	Coverage strength
ShellBar	Dialog without accessible name	Yes	No	ACC-253, ACC-264	"the dialog 'title' should be associated with the container having role=dialog using aria-labelledby"	Direct

[ui5-webcomponents-bot]

🚀 Deployed on https://pr-13556--ui5-webcomponents-preview.netlify.app

[dobrinyonkov]

🟡 Minor — Rule 270 (aria-required on switch host) claimed in PR description is not in this diff

The PR body lists three rule violations, but only Rule 281 (aria-expanded on button host) and Rule 736 (dialog without accessible name) are addressed here. Either:

• Update the PR description to scope it to "search button + overflow dialog", or
• Add the switch fix (the offender is likely in a different template — worth a quick grep).

Not a defect in what's shipped, just a description/scope mismatch worth resolving before merge.