refactor(ui): CardHeading primitive for icon+title card/dialog headings (DRY pattern sweep)

The icon+title v-card-title heading (d-flex align-center + gap + <v-icon size=small> +
<span>) was hand-rolled identically in 13 cards/dialogs (15 heading instances).
Consolidate to <CardHeading icon title> (components/common) with an iconColor
prop (error headings) and a default slot for trailing content (spacer+actions,
inline status chip). Adopted everywhere the pattern appears — all-or-nothing per
the hardened DRY process.

Over-DRY guard: plain text-only <v-card-title> one-liners are NOT this pattern
and stay; DownloadDetailModal leads with a status CHIP (not an icon), a different
concept, left alone. §8b: the only remaining d-flex align-center v-card-title is
that intentional variant. Catalog updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/common/ErrorDetailModal.vue

@@ -2,14 +2,15 @@
   <v-dialog :model-value="modelValue" max-width="900"
             @update:model-value="$emit('update:modelValue', $event)">
     <v-card>
-      <v-card-title class="d-flex align-center" style="gap: 12px;">
-        <v-icon icon="mdi-alert-circle-outline" color="error" />
-        <span>{{ displayTitle }}</span>
+      <CardHeading
+        icon="mdi-alert-circle-outline" icon-color="error"
+        :title="displayTitle"
+      >
         <v-spacer />
         <v-btn icon variant="text" size="small" @click="close">
           <v-icon>mdi-close</v-icon>
         </v-btn>
-      </v-card-title>
+      </CardHeading>
       <v-card-text>
         <dl v-if="contextRows.length" class="fc-err-context">
           <template v-for="(row, idx) in contextRows" :key="idx">
@@ -37,6 +38,7 @@ import { toast } from '../../utils/toast.js'
 import { computed, ref, watch } from 'vue'
 
 import { copyText } from '../../utils/clipboard.js'
+import CardHeading from './CardHeading.vue'
 
 const props = defineProps({
   modelValue: { type: Boolean, default: false },