feat(ui): collapse Downloads filters into compact bar with popover

Replaces two stacked filter rows (4 fields + superseded switch) with a
single "Filters" button that opens a popover containing all controls.
Active filters surface as dismissable chips on the bar alongside a
"Clear all" button, so what's currently applied stays visible without
eating vertical space above the table.

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

frontend/src/views/Downloads.vue

@@ -68,62 +68,120 @@
       </v-col>
     </v-row>
 
-    <!-- Filters -->
-    <v-row class="mb-4">
-      <v-col cols="12" md="3">
-        <v-select
-          v-model="filterStatus"
-          :items="statusOptions"
-          label="Status"
-          density="compact"
-          variant="outlined"
-          clearable
-        />
-      </v-col>
-      <v-col cols="12" md="3">
-        <v-select
-          v-model="filterSourceId"
-          :items="sourceOptions"
-          label="Source"
-          density="compact"
-          variant="outlined"
-          clearable
-        />
-      </v-col>
-      <v-col cols="12" md="3">
-        <v-text-field
-          v-model="filterFromDate"
-          label="From Date"
-          type="date"
-          density="compact"
-          variant="outlined"
-          clearable
-        />
-      </v-col>
-      <v-col cols="12" md="3">
-        <v-text-field
-          v-model="filterToDate"
-          label="To Date"
-          type="date"
-          density="compact"
-          variant="outlined"
-          clearable
-        />
-      </v-col>
-    </v-row>
+    <!-- Filters (compact bar with popover) -->
+    <div class="d-flex align-center flex-wrap ga-2 mb-4">
+      <v-menu :close-on-content-click="false" location="bottom start">
+        <template v-slot:activator="{ props }">
+          <v-btn v-bind="props" variant="outlined" size="small" prepend-icon="mdi-filter-variant">
+            Filters
+            <v-chip v-if="activeFilterCount" class="ml-2" size="x-small" color="primary">
+              {{ activeFilterCount }}
+            </v-chip>
+            <v-icon end>mdi-chevron-down</v-icon>
+          </v-btn>
+        </template>
+        <v-card min-width="320" class="pa-4">
+          <v-select
+            v-model="filterStatus"
+            :items="statusOptions"
+            label="Status"
+            density="compact"
+            variant="outlined"
+            clearable
+            class="mb-2"
+            hide-details
+          />
+          <v-select
+            v-model="filterSourceId"
+            :items="sourceOptions"
+            label="Source"
+            density="compact"
+            variant="outlined"
+            clearable
+            class="mb-2"
+            hide-details
+          />
+          <v-text-field
+            v-model="filterFromDate"
+            label="From Date"
+            type="date"
+            density="compact"
+            variant="outlined"
+            clearable
+            class="mb-2"
+            hide-details
+          />
+          <v-text-field
+            v-model="filterToDate"
+            label="To Date"
+            type="date"
+            density="compact"
+            variant="outlined"
+            clearable
+            class="mb-3"
+            hide-details
+          />
+          <v-switch
+            v-model="filterExcludeSuperseded"
+            label="Hide superseded failures"
+            density="compact"
+            hide-details
+            color="primary"
+          />
+        </v-card>
+      </v-menu>
 
-    <!-- Superseded filter -->
-    <v-row class="mb-4">
-      <v-col cols="12">
-        <v-switch
-          v-model="filterExcludeSuperseded"
-          label="Hide superseded failures"
-          density="compact"
-          hide-details
-          color="primary"
-        />
-      </v-col>
-    </v-row>
+      <!-- Active filter chips -->
+      <v-chip
+        v-if="filterStatus"
+        size="small"
+        closable
+        @click:close="filterStatus = null"
+      >
+        Status: {{ statusLabel(filterStatus) }}
+      </v-chip>
+      <v-chip
+        v-if="filterSourceId"
+        size="small"
+        closable
+        @click:close="filterSourceId = null"
+      >
+        Source: {{ sourceLabel(filterSourceId) }}
+      </v-chip>
+      <v-chip
+        v-if="filterFromDate"
+        size="small"
+        closable
+        @click:close="filterFromDate = null"
+      >
+        From: {{ filterFromDate }}
+      </v-chip>
+      <v-chip
+        v-if="filterToDate"
+        size="small"
+        closable
+        @click:close="filterToDate = null"
+      >
+        To: {{ filterToDate }}
+      </v-chip>
+      <v-chip
+        v-if="!filterExcludeSuperseded"
+        size="small"
+        closable
+        @click:close="filterExcludeSuperseded = true"
+      >
+        Showing superseded
+      </v-chip>
+
+      <v-btn
+        v-if="activeFilterCount"
+        size="small"
+        variant="text"
+        @click="clearAllFilters"
+      >
+        Clear all
+      </v-btn>
+    </div>
 
     <!-- Downloads Table -->
     <v-card>
@@ -334,6 +392,32 @@ const sourceOptions = computed(() =>
   }))
 )
 
+const activeFilterCount = computed(() => {
+  let n = 0
+  if (filterStatus.value) n++
+  if (filterSourceId.value) n++
+  if (filterFromDate.value) n++
+  if (filterToDate.value) n++
+  if (!filterExcludeSuperseded.value) n++
+  return n
+})
+
+function statusLabel(value) {
+  return statusOptions.find(s => s.value === value)?.title || value
+}
+
+function sourceLabel(id) {
+  return sourceOptions.value.find(s => s.value === id)?.title || `#${id}`
+}
+
+function clearAllFilters() {
+  filterStatus.value = null
+  filterSourceId.value = null
+  filterFromDate.value = null
+  filterToDate.value = null
+  filterExcludeSuperseded.value = true
+}
+
 const headers = [
   { title: 'Status', key: 'status', width: 120 },
   { title: 'Source', key: 'source', width: 180 },