feat(ui): show relative timestamps on Dashboard and Downloads tables

Converts the Source Health last-check column and the Downloads created-at
column from locale date strings to human-relative times ("6 hours ago").
The absolute timestamp is preserved as a native browser tooltip so full
precision is still one hover away; detail modals keep the absolute form.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/views/Dashboard.vue

@@ -317,7 +317,7 @@
                   <td>
                     <v-chip color="error" size="small">{{ source.error_count }}</v-chip>
                   </td>
-                  <td>{{ formatDate(source.last_check) }}</td>
+                  <td><span :title="formatDate(source.last_check)">{{ source.last_check ? formatRelativeTime(source.last_check) : 'Never' }}</span></td>
                   <td>
                     <v-btn
                       size="small"

frontend/src/views/Downloads.vue

@@ -148,7 +148,7 @@
         </template>
 
         <template v-slot:item.source="{ item }">
-          <span class="text-caption">{{ getSourceLabel(item.source_id) }}</span>
+          <span class="text-caption">{{ getSourceLabel(item) }}</span>
         </template>
 
         <template v-slot:item.url="{ item }">
@@ -175,7 +175,7 @@
         </template>
 
         <template v-slot:item.created_at="{ item }">
-          {{ formatDate(item.created_at) }}
+          <span :title="formatDate(item.created_at)">{{ formatRelativeTime(item.created_at) }}</span>
         </template>
 
         <template v-slot:item.duration="{ item }">
@@ -234,7 +234,7 @@
             <tbody>
               <tr>
                 <td class="font-weight-bold" width="150">Source</td>
-                <td>{{ getSourceLabel(selectedDownload.source_id) }}</td>
+                <td>{{ getSourceLabel(selectedDownload) }}</td>
               </tr>
               <tr>
                 <td class="font-weight-bold">URL</td>
@@ -444,14 +444,36 @@ function formatDate(dateStr) {
   return new Date(dateStr).toLocaleString()
 }
 
+function formatRelativeTime(dateStr) {
+  if (!dateStr) return '-'
+  const date = new Date(dateStr)
+  const now = new Date()
+  const diffMs = now - date
+  const diffMins = Math.floor(diffMs / 60000)
+  const diffHours = Math.floor(diffMs / 3600000)
+  const diffDays = Math.floor(diffMs / 86400000)
+
+  if (diffMins < 1) return 'Just now'
+  if (diffMins < 60) return `${diffMins} min${diffMins !== 1 ? 's' : ''} ago`
+  if (diffHours < 24) return `${diffHours} hour${diffHours !== 1 ? 's' : ''} ago`
+  if (diffDays < 7) return `${diffDays} day${diffDays !== 1 ? 's' : ''} ago`
+  return date.toLocaleDateString()
+}
+
 function formatDuration(download) {
-  if (!download.started_at || !download.completed_at) return '-'
+  if (!download.started_at) return '-'
   const start = new Date(download.started_at)
-  const end = new Date(download.completed_at)
+  // Running rows elapse against "now"; terminal rows need a valid completed_at.
+  const end = download.status === 'running' || !download.completed_at
+    ? new Date()
+    : new Date(download.completed_at)
   const seconds = Math.round((end - start) / 1000)
+  if (seconds < 0) return '-'
   if (seconds < 60) return `${seconds}s`
   const minutes = Math.floor(seconds / 60)
-  return `${minutes}m ${seconds % 60}s`
+  if (minutes < 60) return `${minutes}m ${seconds % 60}s`
+  const hours = Math.floor(minutes / 60)
+  return `${hours}h ${minutes % 60}m`
 }
 
 function formatErrorType(errorType) {
@@ -465,7 +487,18 @@ function truncateUrl(url) {
   return url.substring(0, 37) + '...'
 }
 
-function getSourceLabel(sourceId) {
+function getSourceLabel(item) {
+  // Prefer the subscription_name/platform embedded in the download record —
+  // these survive source deletion and don't require the sources store to be populated.
+  if (item && typeof item === 'object') {
+    if (item.subscription_name && item.platform) {
+      return `${item.subscription_name}:${item.platform}`
+    }
+    if (item.platform) {
+      return `(unnamed):${item.platform}`
+    }
+  }
+  const sourceId = typeof item === 'number' ? item : item?.source_id
   if (!sourceId) return 'N/A'
   const source = sourcesStore.sources.find(s => s.id === sourceId)
   if (source) {