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/views.py

@@ -4,7 +4,7 @@ from urllib.parse import urlparse
 
 from django.conf import settings
 from django.core import signing
-from django.db.models import Min
+from django.db.models import Min, Q
 from django.http import Http404, StreamingHttpResponse
 from django.shortcuts import get_object_or_404
 from django.utils import timezone
@@ -51,8 +51,20 @@ class MediaItemViewSet(
                     numeric_ids.append(int(number))
             queryset = queryset.filter(pk__in=numeric_ids)
         search = self.request.query_params.get("search", "").strip()
+        search_type = self.request.query_params.get("search_type", "filename").strip()
         if search:
-            queryset = queryset.filter(locations__rel_path__icontains=search)
+            words = [word for word in search.lower().split() if word]
+            if search_type == "tags":
+                for word in words:
+                    queryset = queryset.filter(search_tags__icontains=word)
+            elif search_type == "both":
+                query = Q(locations__rel_path__icontains=search)
+                tag_query = Q()
+                for word in words:
+                    tag_query &= Q(search_tags__icontains=word)
+                queryset = queryset.filter(query | tag_query)
+            else:
+                queryset = queryset.filter(locations__rel_path__icontains=search)
         ratings = [
             value
             for value in self.request.query_params.get("rating", "").split(",")
@@ -60,6 +72,25 @@ class MediaItemViewSet(
         ]
         if ratings:
             queryset = queryset.filter(rating__in=ratings)
+        statuses = []
+        for value in self.request.query_params.getlist("status"):
+            statuses.extend(
+                part.strip() for part in value.split(",") if part.strip()
+            )
+        if statuses:
+            status_query = Q()
+            for status_value in set(statuses):
+                if status_value == "custom":
+                    status_query |= Q(has_custom_data=True)
+                elif status_value == "matched":
+                    status_query |= Q(
+                        has_custom_data=False, e621_post_id__isnull=False
+                    )
+                elif status_value == "unknown":
+                    status_query |= Q(
+                        has_custom_data=False, e621_post_id__isnull=True
+                    )
+            queryset = queryset.filter(status_query)
         ordering = self.request.query_params.get("ordering", "").strip()
         queryset = queryset.order_by(
             ordering if ordering in LIST_ORDERINGS else "-created_at"