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/api/feed.ts

@@ -2,6 +2,7 @@
 // the shared FeedFilters into the query string the feed + facet endpoints both consume; they stay
 // module-local (no consumer names them). Only touches core's req/beacon.
 import { req, beacon } from "./core";
+import { TAG_CATEGORIES, type TagModes } from "./tagModes";
 
 // Per-user watch status stored server-side (VALID_STATES in routes/feed.py). "in_progress" and
 // "unwatched" are NOT statuses — they're derived feed filters (status "new" + a resume position),
@@ -54,7 +55,8 @@ export interface FeedResponse {
 
 export interface FeedFilters {
   tags: number[];
-  tagMode: "or" | "and";
+  /** Per-category tag match (language / topic / other each independently any/all). */
+  tagModes: TagModes;
   q: string;
   sort: string;
   // Re-roll token for the "shuffle" sort; bumped by the reshuffle button so the
@@ -83,7 +85,10 @@ export interface FeedFilters {
 function filterParams(f: FeedFilters): URLSearchParams {
   const p = new URLSearchParams();
   f.tags.forEach((t) => p.append("tags", String(t)));
-  p.set("tag_mode", f.tagMode);
+  // Only emit the categories set to "and"; the backend defaults each to "or".
+  for (const cat of TAG_CATEGORIES) {
+    if (f.tagModes[cat] === "and") p.set(`tag_mode_${cat}`, "and");
+  }
   if (f.q) p.set("q", f.q);
   p.set("scope", f.scope);
   p.set("show_normal", String(f.includeNormal));