feat: render banners at 100% width when dimensions omitted

[anonvt]

Summary

• When <topsort-banner> is rendered without width/height attributes, the component defaulted to width=0 / height=0, producing an <img> with style=\"width:0px; height:0px\" — invisible to users but still tagged with data-ts-clickable / data-ts-resolved-bid, so analytics.js would record impressions on a zero-pixel banner.
• Treat 0 as a "not set" sentinel and substitute width:100% / height:auto on the rendered <img> / <hls-video> and on the --ts-banner-width / --ts-banner-height host CSS variables. The banner now fills its container at the asset's native aspect ratio when dimensions are omitted.
• The /v2/auctions request is unchanged — width/height were never part of the payload.

Reproducer

<topsort-banner id=\"teste-busca\" search-query=\"pontos\" style=\"margin: 20px 0;\">
</topsort-banner>

Before: auction succeeds, but the rendered <img> is width:0px; height:0px (invisible, still billed).
After: rendered <img> is width:100%; height:auto and visually fills its container.

Behavior change

This is a minor behavior change for integrations that omit width/height — they will now render a visible banner instead of an invisible one. Customers who set explicit dimensions are unaffected. Per-axis fallback works too: e.g. width=\"300\" with no height renders width:300px; height:auto.

Test plan

• pnpm lint — passes (only the pre-existing biome.json warning unrelated to this change)
• pnpm test:run — 106/106 passing, including 4 new regression tests
• Manually verify in the demo app that a <topsort-banner> without width/height renders at the container's width

New regression tests

In src/__tests__/topsort-banner.test.ts:

• standalone banner: <img> style is width:100%; height:auto when attributes omitted
• standalone banner: host CSS vars are --ts-banner-width:100% / --ts-banner-height:auto
• per-axis fallback: width set + height omitted ⇒ height:auto only
• context-mode slots inherit responsive defaults when parent has no dimensions

Each of these fails on main (asserts 100%/auto where current code produces 0px).

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