feat(feed): per-category any/all tag match, in each combobox's popover footer

The tag 'Match: Any/All' toggle was a single GLOBAL setting that only ever
affected topics, shown as its own row under the Topic widget. Make it
per-category — language, topic, and 'your tags' each get their own independent
any/all — and move it into each filter combobox's popover footer (like
SortControl's direction segment), reclaiming the standalone Match row.

Backend: the feed query already groups selected tags by category; replace the
single tag_mode with per-category tag_mode_language/topic/other params and apply
the conjunctive (HAVING all) branch per category. Mirrored across filtered_query,
feed_summary.passes(), and the /facets drill-down exclusion (kept in lockstep;
equivalence test updated to tag_mode_topic). No schema change.

Frontend: FeedFilters.tagMode -> tagModes {language,topic,other} (pure leaf
lib/api/tagModes with a coerceTagModes migration for the legacy global value);
serialized to the API and the shareable URL per category (legacy ?tagmode=and
still resolves into the topic slot); saved-view blobs migrate on read. Combobox
gains an optional matchMode/onMatchModeChange footer segment, shown once 2+
values are picked; the three tag comboboxes wire it to their category.

Verified: backend feed tests green (12, incl. the count/facets equivalence net);
live, the footer appears at 2+ selections, toggles aria-pressed, serializes
tagmode_topic=and to the URL, and the request carries tag_mode_topic=and (200).
374 vitest, tsc, ruff, eslint (0 err).

backend/app/routes/feed.py

@@ -48,7 +48,11 @@ FINISH_MARGIN_SECONDS = 10
 # Shared query parameters for /feed and /feed/count.
 def _feed_params(
     tags: list[int] = Query(default=[]),
-    tag_mode: str = "or",
+    # Per-category tag match: each of language / topic / other independently ORs (any) or ANDs (all)
+    # its own selected tags. Defaults to "or". (Superseded the single global `tag_mode`.)
+    tag_mode_language: str = "or",
+    tag_mode_topic: str = "or",
+    tag_mode_other: str = "or",
     channel_ids: list[str] = Query(default=[]),
     q: str | None = None,
     min_duration: int | None = None,
@@ -65,7 +69,11 @@ def _feed_params(
 ) -> dict:
     return {
         "tags": tags,
-        "tag_mode": tag_mode,
+        "tag_modes": {
+            "language": tag_mode_language,
+            "topic": tag_mode_topic,
+            "other": tag_mode_other,
+        },
         "channel_ids": channel_ids,
         "q": q,
         "min_duration": min_duration,
@@ -162,7 +170,7 @@ def get_facets(
         # independent counts (you can OR more of them in). Conjunctive (AND, topics only)
         # keeps them applied, so each remaining chip narrows to channels that ALSO have all
         # already-selected topics — and tags that can't co-occur drop to zero (hidden).
-        conjunctive = category == "topic" and params.get("tag_mode") == "and"
+        conjunctive = params.get("tag_modes", {}).get(category) == "and"
         base, _rank = filtered_query(
             db,
             user,