feat(downloads): copy buttons in the download detail modal

Operator-flagged 2026-05-28: the download event detail modal had no way
to copy the error / stdout / stderr text for researching a failure
(parity with the ErrorDetailModal Copy button shipped in v26.05.26.0).

Added per-block Copy buttons (Error, Errors & warnings, Raw stdout, Raw
stderr — the stdout/stderr ones sit in the expansion-panel title with
@click.stop so they don't toggle the panel) plus a "Copy all
diagnostics" button in the footer that assembles a single block: header
line (event id / platform / artist / status / timestamps) + error +
errors&warnings + full stdout + stderr, ready to paste into an issue.

All routed through utils/clipboard.js copyText() — the navigator.clipboard
→ execCommand fallback that works on the plain-HTTP homelab origin
(per feedback_no_secure_context_apis). Each copy shows a confirmation
toast.

frontend/src/components/downloads/DownloadDetailModal.vue

@@ -35,20 +35,53 @@
           </ul>
         </template>
 
+        <template v-if="event.error">
+          <div class="fc-dl-blockhead mt-4">
+            <h3 class="text-subtitle-2">Error</h3>
+            <v-btn
+              size="x-small" variant="text" prepend-icon="mdi-content-copy"
+              @click="onCopy('Error', event.error)"
+            >Copy</v-btn>
+          </div>
+          <pre class="fc-dl-pre">{{ event.error }}</pre>
+        </template>
+
         <template v-if="errorsWarnings">
-          <h3 class="text-subtitle-2 mt-4">Errors &amp; warnings</h3>
+          <div class="fc-dl-blockhead mt-4">
+            <h3 class="text-subtitle-2">Errors &amp; warnings</h3>
+            <v-btn
+              size="x-small" variant="text" prepend-icon="mdi-content-copy"
+              @click="onCopy('Errors & warnings', errorsWarnings)"
+            >Copy</v-btn>
+          </div>
           <pre class="fc-dl-pre">{{ errorsWarnings }}</pre>
         </template>
 
         <v-expansion-panels class="mt-4">
           <v-expansion-panel>
-            <v-expansion-panel-title>Raw stdout</v-expansion-panel-title>
+            <v-expansion-panel-title>
+              <span>Raw stdout</span>
+              <v-spacer />
+              <v-btn
+                size="x-small" variant="text" prepend-icon="mdi-content-copy"
+                class="me-2"
+                @click.stop="onCopy('stdout', event.metadata?.stdout || '')"
+              >Copy</v-btn>
+            </v-expansion-panel-title>
             <v-expansion-panel-text>
               <pre class="fc-dl-pre">{{ event.metadata?.stdout || '(empty)' }}</pre>
             </v-expansion-panel-text>
           </v-expansion-panel>
           <v-expansion-panel>
-            <v-expansion-panel-title>Raw stderr</v-expansion-panel-title>
+            <v-expansion-panel-title>
+              <span>Raw stderr</span>
+              <v-spacer />
+              <v-btn
+                size="x-small" variant="text" prepend-icon="mdi-content-copy"
+                class="me-2"
+                @click.stop="onCopy('stderr', event.metadata?.stderr || '')"
+              >Copy</v-btn>
+            </v-expansion-panel-title>
             <v-expansion-panel-text>
               <pre class="fc-dl-pre">{{ event.metadata?.stderr || '(empty)' }}</pre>
             </v-expansion-panel-text>
@@ -56,6 +89,10 @@
         </v-expansion-panels>
       </v-card-text>
       <v-card-actions>
+        <v-btn
+          variant="text" prepend-icon="mdi-content-copy"
+          @click="onCopy('All diagnostics', allDiagnostics)"
+        >Copy all diagnostics</v-btn>
         <v-spacer />
         <v-btn variant="text" @click="onClose(false)">Close</v-btn>
       </v-card-actions>
@@ -66,6 +103,8 @@
 <script setup>
 import { computed } from 'vue'
 
+import { copyText } from '../../utils/clipboard.js'
+
 const props = defineProps({ event: { type: Object, default: null } })
 const emit = defineEmits(['close'])
 
@@ -74,6 +113,32 @@ const summary = computed(() => props.event?.metadata?.import_summary || {})
 const quarantinedPaths = computed(() => props.event?.metadata?.quarantined_paths || [])
 const errorsWarnings = computed(() => props.event?.metadata?.stderr_errors_warnings || '')
 
+// One combined block for "research the issue elsewhere" — header line +
+// error + full stdout/stderr. Built lazily from the current event.
+const allDiagnostics = computed(() => {
+  const e = props.event
+  if (!e) return ''
+  const md = e.metadata || {}
+  return [
+    `event #${e.id} · ${e.platform || '—'} · ${e.artist_name || '—'}`,
+    `status: ${e.status}`,
+    `started: ${e.started_at}  finished: ${e.finished_at || '(running)'}`,
+    e.error ? `\n--- error ---\n${e.error}` : '',
+    errorsWarnings.value ? `\n--- errors & warnings ---\n${errorsWarnings.value}` : '',
+    `\n--- stdout ---\n${md.stdout || '(empty)'}`,
+    `\n--- stderr ---\n${md.stderr || '(empty)'}`,
+  ].filter(Boolean).join('\n')
+})
+
+async function onCopy(label, text) {
+  try {
+    await copyText(text || '')
+    window.__fcToast?.({ text: `${label} copied`, type: 'success' })
+  } catch (e) {
+    window.__fcToast?.({ text: `Copy failed: ${e.message}`, type: 'error' })
+  }
+}
+
 const statusColor = computed(() => ({
   ok: 'success', error: 'error', running: 'info',
   pending: 'secondary', skipped: 'warning',
@@ -114,4 +179,8 @@ function onClose() {
   word-break: break-all;
 }
 .fc-dl-quar { padding-left: 1.5rem; font-size: 0.85rem; }
+.fc-dl-blockhead {
+  display: flex; align-items: center; justify-content: space-between;
+  gap: 0.5rem;
+}
 </style>