fix(ui) : phase 1 review fixes — machine context links, type annotations, double arrow

- Add ?from=machine&machineId=xxx query params to entity NuxtLinks in hierarchy
- Add useRoute + machineId computed to ComponentItem, PieceItem, MachineProductsCard
- Add :string type to confirmRemove* handlers in machine page
- Remove unicode arrow from DetailHeader backLabel (icon already provides it)
- Add !isEditMode guard on product links in MachineProductsCard

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/app/components/PieceItem.vue

@@ -31,7 +31,9 @@
           <h3 class="text-lg font-semibold" :class="{ 'text-error': piece._emptySlot || piece.pendingEntity }">
             <NuxtLink
               v-if="!isEditMode && !piece.pendingEntity && !piece._emptySlot && piece.pieceId"
-              :to="`/piece/${piece.pieceId}`"
+              :to="machineId
+                ? { path: `/piece/${piece.pieceId}`, query: { from: 'machine', machineId } }
+                : `/piece/${piece.pieceId}`"
               class="hover:underline hover:text-primary transition-colors"
               @click.stop
             >
@@ -332,6 +334,9 @@ import { useCustomFields } from '~/composables/useCustomFields'
 import { useEntityDocuments } from '~/composables/useEntityDocuments'
 import { useEntityProductDisplay } from '~/composables/useEntityProductDisplay'
 
+const route = useRoute()
+const machineId = computed(() => route.params.id as string | undefined)
+
 const props = defineProps({
   piece: { type: Object, required: true },
   isEditMode: { type: Boolean, default: false },