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).

frontend/src/lib/urlState.ts

@@ -4,7 +4,7 @@
 // bookmarkable/shareable — the old "Share view" workaround (and the whole-query stripUrlParams) is
 // retired. Only non-default values are emitted so URLs stay clean. NOTE: the browser TAB title stays
 // the short module/channel name (NavigationProvider owns document.title) — the query never leaks into it.
-import type { FeedFilters } from "./api";
+import { TAG_CATEGORIES, type FeedFilters } from "./api";
 
 const KEYS = [
   "q",
@@ -16,7 +16,10 @@ const KEYS = [
   "shorts",
   "live",
   "tags",
-  "tagmode",
+  "tagmode_language",
+  "tagmode_topic",
+  "tagmode_other",
+  "tagmode", // legacy global (topic-only) — still recognised so old shared links resolve
   "channel",
   "maxage",
   "from",
@@ -38,7 +41,9 @@ export function filtersToParams(f: FeedFilters): URLSearchParams {
   if (f.includeShorts) p.set("shorts", "1");
   if (f.includeLive) p.set("live", "1");
   if (f.tags.length) p.set("tags", f.tags.join(","));
-  if (f.tagMode === "and") p.set("tagmode", "and");
+  for (const cat of TAG_CATEGORIES) {
+    if (f.tagModes[cat] === "and") p.set(`tagmode_${cat}`, "and");
+  }
   if (f.channelIds.length) p.set("channel", f.channelIds.join(","));
   if (f.maxAgeDays) p.set("maxage", String(f.maxAgeDays));
   if (f.dateFrom) p.set("from", f.dateFrom);
@@ -84,7 +89,12 @@ export function paramsToFilters(params: URLSearchParams, base: FeedFilters): Fee
       .split(",")
       .map((s) => Number(s))
       .filter((n) => Number.isInteger(n));
-  if (params.has("tagmode")) f.tagMode = params.get("tagmode") === "and" ? "and" : "or";
+  // Per-category tag match; a legacy global `tagmode=and` (topic-only) migrates into the topic slot.
+  f.tagModes = {
+    language: params.get("tagmode_language") === "and" ? "and" : "or",
+    topic: params.get("tagmode_topic") === "and" || params.get("tagmode") === "and" ? "and" : "or",
+    other: params.get("tagmode_other") === "and" ? "and" : "or",
+  };
   f.channelIds = (params.get("channel") ?? "").split(",").filter(Boolean);
   f.maxAgeDays = num(params.get("maxage"));
   f.dateFrom = params.get("from") || undefined;