ui: the STK menu button shows the title without the "STK: " prefix

The Simulator view's "STK menu" block already carries the legend, so the
emerald button's hardcoded "STK: " prefix was redundant.  It now shows just
the card's menu title (e.g. "Alfa Mobile"), or "Menu"/"Меню" for a
title-less SET UP MENU (`stkMenuLabel`, unchanged).

The help pages (EN/RU) describe the button as the menu title, both AGENTS
files drop the old `STK: Menu` wording, and stk_menu.test.js gains a source
guard against the prefix returning.  sw cache simple-v341.
Tests: 743 Node / 619 Python.

frontend/tests/stk_menu.test.js

@@ -194,3 +194,9 @@ test('stkMenuLabel shows the card title or a generic label', () => {
 	assert.strictEqual(stkMenuLabel({ items: [] }), '');
 	assert.strictEqual(stkMenuLabel(null), '');
 });
+
+test('the STK menu button shows the title without an STK: prefix', () => {
+	// the block's legend already says "STK menu" - the prefix was redundant
+	assert.match(html, /id="stk-menu-btn"[^>]*><span id="stk-menu-title"><\/span><\/button>/);
+	assert.ok(!/>STK: </.test(html), 'the redundant "STK: " prefix must be gone');
+});