feat: gallery + generic blueprint viewer, add Grid blueprint

Refactor the List-specific screen into a data-driven, reusable viewer:
- generic Blueprint type + shared LoadState machine + registry
- vue-router: / (gallery) and /b/:slug (illustration)
- BlueprintViewer renders any blueprint; specimens stay bespoke
- add Grid blueprint (6 functions incl. Position) + GridSpecimen

src/data/blueprints.ts

@@ -0,0 +1,26 @@
+// Registry: the single source the router and Gallery both read from. A blueprint
+// appears in the app precisely when it is registered here — pairing its typed data
+// with its bespoke Specimen component.
+
+import type { Component } from "vue"
+import type { Blueprint } from "./blueprint"
+import { list } from "./listBlueprint"
+import { grid } from "./gridBlueprint"
+import ListSpecimen from "@/specimens/ListSpecimen.vue"
+import GridSpecimen from "@/specimens/GridSpecimen.vue"
+
+export interface RegistryEntry {
+  blueprint: Blueprint
+  specimen: Component
+}
+
+export const REGISTRY: Record<string, RegistryEntry> = {
+  list: { blueprint: list, specimen: ListSpecimen },
+  grid: { blueprint: grid, specimen: GridSpecimen },
+}
+
+export const BLUEPRINTS: Blueprint[] = Object.values(REGISTRY).map((e) => e.blueprint)
+
+export function entryFor(slug: string): RegistryEntry | undefined {
+  return REGISTRY[slug]
+}