feat(series): Suggestions tab + matcher controls — frontend (FC-6.3)

Completes FC-6.3 with the UI.

- SeriesView gains tabs: Browse (the existing grid) + Suggestions.
- Suggestions tab: pending matches as rows (post → series, per-signal strength
  chips, score), Add (→ chapter) / Skip (→ dismiss); a "Matching on" toggle and
  a threshold field (both DB-backed via /settings/import), and a Rescan button
  that enqueues the background matcher.
- seriesSuggestions store wires load / accept / dismiss / rescan / settings.

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

frontend/src/stores/seriesSuggestions.js

@@ -0,0 +1,75 @@
+import { defineStore } from 'pinia'
+import { ref } from 'vue'
+import { useApi } from '../composables/useApi.js'
+import { useAsyncAction } from '../composables/useAsyncAction.js'
+import { toast } from '../utils/toast.js'
+
+// Backs the Series → Suggestions tab (FC-6.3). The matcher is confirm-only:
+// accept turns a suggestion into a chapter; skip dismisses it. enabled +
+// threshold are the operator-tunable knobs (DB-backed via /settings/import).
+export const useSeriesSuggestionsStore = defineStore('seriesSuggestions', () => {
+  const api = useApi()
+  const suggestions = ref([])
+  const enabled = ref(true)
+  const threshold = ref(0.5)
+  const { loading, error, run } = useAsyncAction({ errorAs: 'message' })
+
+  async function load() {
+    await run(async () => {
+      const body = await api.get('/api/series/suggestions')
+      suggestions.value = body.suggestions || []
+    })
+  }
+
+  async function loadSettings() {
+    const s = await api.get('/api/settings/import')
+    enabled.value = s.series_suggest_enabled
+    threshold.value = s.series_suggest_threshold
+  }
+
+  async function saveSettings(patch) {
+    await api.patch('/api/settings/import', { body: patch })
+  }
+
+  async function setEnabled(v) {
+    enabled.value = v
+    await saveSettings({ series_suggest_enabled: v })
+  }
+
+  async function setThreshold(v) {
+    threshold.value = v
+    await saveSettings({ series_suggest_threshold: v })
+  }
+
+  async function accept(id) {
+    try {
+      await api.post(`/api/series/suggestions/${id}/accept`, {})
+      suggestions.value = suggestions.value.filter(s => s.id !== id)
+      toast({ text: 'Added to series', type: 'success' })
+    } catch (e) {
+      toast({ text: `Accept failed: ${e.message}`, type: 'error' })
+    }
+  }
+
+  async function dismiss(id) {
+    try {
+      await api.post(`/api/series/suggestions/${id}/dismiss`, {})
+      suggestions.value = suggestions.value.filter(s => s.id !== id)
+    } catch (e) {
+      toast({ text: `Skip failed: ${e.message}`, type: 'error' })
+    }
+  }
+
+  async function rescan() {
+    await api.post('/api/series/suggestions/rescan', {})
+    toast({
+      text: 'Rescan queued — runs in the background; reload to see new matches.',
+      type: 'info'
+    })
+  }
+
+  return {
+    suggestions, enabled, threshold, loading, error,
+    load, loadSettings, setEnabled, setThreshold, accept, dismiss, rescan
+  }
+})