Library search upgrades: tag search, tag cloud, status filter

Backend:
- MediaItem gains search_tags (custom + e621 tags, lowercase) and
  has_custom_data, maintained on save with a data migration backfill
- File list search accepts search_type=filename|tags|both (tag search is
  word-AND across the flattened tag text) and status=matched|custom|
  unknown filters
- New /api/tags/cloud/ endpoint (cached 2 min per guest/auth, invalidated
  on item changes and deletions) returning the most-used tags, honouring
  guest visibility

Frontend:
- Library sidebar: Filename/Tags/Both selector, status pill toggles
  (persisted), and a clickable tag cloud that runs a tag search
- Roadmap updated

backend/apps/library/tools.py

@@ -8,11 +8,11 @@ from django.conf import settings
 from django.core.cache import cache
 from django.db.models import Count, Q
 from rest_framework import status
-from rest_framework.permissions import IsAuthenticated
+from rest_framework.permissions import AllowAny, IsAuthenticated
 from rest_framework.response import Response
 from rest_framework.views import APIView
 
-from .models import MediaItem, MediaLocation
+from .models import TAG_CLOUD_CACHE_KEYS, MediaItem, MediaLocation
 from .permissions import CanUpload
 
 logger = logging.getLogger(__name__)
@@ -299,6 +299,7 @@ class DeleteFilesView(APIView):
             item.delete()
 
         cache.delete(STORAGE_CACHE_KEY)
+        cache.delete_many(TAG_CLOUD_CACHE_KEYS)
 
         for location in MediaLocation.objects.filter(
             id__in=location_ids
@@ -338,6 +339,56 @@ class ClearTempView(APIView):
         return Response({"removed": removed})
 
 
+class TagCloudView(APIView):
+    """Most-used tags across the library (custom + e621 tags)."""
+
+    permission_classes = [AllowAny]
+
+    def get(self, request):
+        cache_key = (
+            "j621.library.tag_cloud.auth"
+            if request.user.is_authenticated
+            else "j621.library.tag_cloud.guest"
+        )
+        cached = cache.get(cache_key)
+        if cached is not None:
+            return Response(cached)
+
+        queryset = MediaItem.objects.all()
+        if not request.user.is_authenticated:
+            queryset = queryset.filter(hidden_from_guests=False)
+
+        counts = {}
+        for item in queryset.only("tags", "e621_data").iterator(chunk_size=500):
+            names = set()
+            for tag in item.tags or []:
+                name = str(tag).strip().lower()
+                if name:
+                    names.add(name)
+            data = item.e621_data or {}
+            categories = data.get("tags") if isinstance(data, dict) else None
+            if isinstance(categories, dict):
+                for values in categories.values():
+                    if isinstance(values, list):
+                        names.update(
+                            str(tag).strip().lower()
+                            for tag in values
+                            if str(tag).strip()
+                        )
+            for name in names:
+                counts[name] = counts.get(name, 0) + 1
+
+        ranked = sorted(counts.items(), key=lambda entry: (-entry[1], entry[0]))
+        payload = {
+            "count": len(counts),
+            "tags": [
+                {"tag": tag, "count": count} for tag, count in ranked[:120]
+            ],
+        }
+        cache.set(cache_key, payload, 120)
+        return Response(payload)
+
+
 class StorageView(APIView):
     """Disk usage for the watched folder, media root and temp uploads."""