fix(header): remove duplicate-looking mobile menu icon (BUY-64576)

[BuyWhere]

Summary

• remove the blue three-line SVG from the BuyWhere brand link; it visually duplicated the real mobile hamburger
• keep the single functional menu toggle on the right
• cover 390×844 mobile and 768×1024 tablet layouts in Playwright

Verification

Runtime-observed the modified homepage in Chromium:

• 390×844: plain BuyWhere brand, zero SVGs in brand link, exactly one visible Open menu button
• 768×1024: same
• clicked the toggle at both sizes: Close menu appeared and the mobile drawer was visible
• 1280×800 probe: menu toggle hidden, full main navigation visible

next build --no-lint compiled the source and completed type validation. The default build lint phase remains blocked by pre-existing unused Metadata imports across unrelated pages.

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