Unify pin ordering: WorkflowGrid re-sort vs use-case-resolver dedup have opposite duplicate semantics

Follow-up from review on #1057.

`WorkflowGrid.vue` builds `pinRank = new Map(pinnedShareIds.map((id, i) => [id, i]))`, which keeps the LAST index for a repeated key, while `use-case-resolver.ts` dedupes pins first-wins. `[slug].astro` feeds raw `def.pins` (not the resolved list), so the two derivations can drift. Latent today (no page repeats a pin), and the client re-sort is genuinely required.

Proposed: extract one `orderByPins(templates, pinnedShareIds)` pure function used by both the resolver and the WorkflowGrid re-sort, with a unit test (the ordering is currently untested).

Reported by @MaanilVerma.

Start by reading WorkflowGrid.vue, use-case-resolver.ts, and [slug].astro to trace how pin ordering is derived from raw and resolved lists. Add the shared ordering behavior and a unit test covering duplicate pins; done means both derivations use the same ordering semantics and the test passes.

Written by the indexing model from the issue text.