Add SSR'd `/compare/[a]-vs-[b]` head-to-head GPU comparison pages

[adibarra]

Per-pair GPU comparison pages, SSR'd so they're indexable and link-shareable, working for any valid combination of GPUs in the registry.

Example slugs:

• /compare/h100-vs-h200
• /compare/mi300x-vs-h200
• /compare/b200-vs-mi325x
• /compare/gb200-vs-h100

Requirements

• Works with any pair of GPUs in HW_REGISTRY. Slug format and canonicalization (e.g. alphabetical, inverse redirects to canonical) is open.
• SSR so the page and data are indexable. Use dynamic SSR so it reflects the latest data. Cache invalidation should hook into the existing invalidate endpoint rather than time-based revalidation.
• JSON-LD on the page so LLMs and search engines can consume the comparison data.
• Chart of the two GPUs' performance with the same controls as /inference: y-axis, model, precision, etc. Same pan/zoom interactions and download PNG / CSV buttons as the rest of the site's charts.
• Data table below the chart showing the underlying numbers.
• Visual design should match the rest of the site closely while leaving room for creative freedom as to the actual page's design.
• The chart should use the same shared d3 library that the rest of the charts on the site use, feel free to extend it with any new features.

Nice to have

• OG image generator similar to the blog pages', scoped to comparisons.