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/views/BlueprintView.vue

@@ -0,0 +1,40 @@
+<script setup lang="ts">
+import { computed } from "vue"
+import { entryFor } from "@/data/blueprints"
+import BlueprintViewer from "@/components/BlueprintViewer.vue"
+
+const props = defineProps<{ slug: string }>()
+const entry = computed(() => entryFor(props.slug))
+</script>
+
+<template>
+  <BlueprintViewer v-if="entry" :blueprint="entry.blueprint" :specimen="entry.specimen" />
+  <div v-else class="notfound">
+    <p>
+      No blueprint <code>{{ slug }}</code> is illustrated yet.
+    </p>
+    <RouterLink to="/" class="back">▸ back to the gallery</RouterLink>
+  </div>
+</template>
+
+<style scoped>
+.notfound {
+  max-width: 1180px;
+  margin: 0 auto;
+  padding: 60px 20px;
+  color: #9db8d2;
+  text-align: center;
+}
+.notfound code {
+  color: var(--color-accent);
+}
+.back {
+  display: inline-block;
+  margin-top: 14px;
+  color: var(--color-secondary);
+  text-decoration: none;
+}
+.back:hover {
+  text-decoration: underline;
+}
+</style>