feat(ui): replace native confirm() with DaisyUI modal composable (F7.2)

Create useConfirm composable (promise-based, singleton state) and
ConfirmModal component. Replace all 10 confirm()/window.confirm() calls
across 9 pages and 1 composable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/pages/pieces-catalog.vue

@@ -189,7 +189,7 @@
 </template>
 
 <script setup lang="ts">
-import { computed, onMounted, ref, watch } from 'vue'
+import { computed, onMounted, ref } from 'vue'
 import { usePieces } from '~/composables/usePieces'
 import { usePieceTypes } from '~/composables/usePieceTypes'
 import { useToast } from '~/composables/useToast'
@@ -442,7 +442,8 @@ const handleDeletePiece = async (piece: Record<string, any>) => {
     )
   }
 
-  const confirmed = window.confirm(confirmLines.join('\n\n'))
+  const { confirm } = useConfirm()
+  const confirmed = await confirm({ message: confirmLines.join('\n\n') })
   if (!confirmed) {
     return
   }