hotfix(main): restore categories.ts + add venue dimension

[Flotapponnier]

What

Main prod was failing typecheck on two unrelated cherry-picks:

1. PR feat(seo): /benchmarks/category/[cat] hub pages (D.2) #743 imported `@/lib/categories` but the file itself was never cherry-picked.
2. PR chore: cherry-pick worker venue dimension materialization #731 cherry-picked worker code using a `venue` dimension but the spec schema + `BenchmarkFilters` type were never extended.

Fix

• Add `src/lib/categories.ts` (copied from dev).
• Add `venue` to `SpecSchema.dimensions`.
• Add `venue?: string` to `BenchmarkFilters` + handle in `parseFilterSig`.

`pnpm typecheck` green.