fix(BUY-64580): clean robot vacuum catalog cards

[BuyWhere]

Summary

• constrain the robot-vacuum SEO snapshot with the upstream category filter plus a strict complete-floor-robot classifier
• reject parts, accessories, stick/pool vacuums, and the known failing elescat image host while preserving the existing image placeholder
• use compact two-column cards so title, merchant, price, and CTA are visible without clipping and the first desktop card fits in a 1440×900 viewport

Verification

• npx tsx --test --test-name-pattern="robot-vacuum|non-robot landing" src/lib/seo-landing-pages.test.ts — 4/4 passed
• targeted Next lint — passed
• deploy-like Playwright run at 1440×900 and 390×844 — 8/8 complete robot vacuums, all metadata/CTAs present, no clipping/overflow, no elescat request
• forced all product-image requests to fail — 8/8 cards rendered fallback placeholders with zero broken <img> elements

Known unrelated gates

• Full SEO test file still has the pre-existing iphone-16-price-singapore fallback-image failure.
• Default next build is blocked by pre-existing unused Metadata imports on unrelated pages; next build --no-lint succeeds.

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