feat(feed): make For You inclusive + ranked by your lists (G1-G5)

The For You feed was chronological, hashtag-interest-EXCLUSIVE, and ignored
follows entirely (docs/feed-algo-audit.md). Now it is inclusive + ranked:

- createForYouScorerStage scores each video: follows-boost (author you follow)
  + interest/watch-topic affinity (cosine vs your interests+watch-history vector)
  + freshness - disinterest penalty. Reuses Explore's vector/similarity helpers.
- createForYouScoreSorter ranks by that score (muted last, recency tiebreak).
- For You pipeline: interests now BOOST not exclude (enforceInterests:false);
  scorer added; chronological sorter replaced. Never empty (falls back to
  recency when you have no follows/interests/history).
- buildForYouFeedRuntime now feeds subscriptionAuthors + watchHistoryTagCounts.

Watched/blocked/muted are still removed (suppression/blacklist/moderation
stages unchanged). Cheat-resistant tests (older boosted items only win via the
boost). Grid renders end-to-end (~1.3s). Weight tuning is a follow-up.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/feedEngine/sorters.js

@@ -3,6 +3,54 @@
 import { normalizeHashtag } from "../utils/hashtagNormalization.js";
 import { markAsNormalized } from "./utils.js";
 
+// Ranks by the For You score (set by createForYouScorerStage): score desc,
+// trusted-muted last, recency as the tiebreak. Reuses the same muted-last rule
+// as the chronological sorter so behavior is consistent across feeds.
+export function createForYouScoreSorter() {
+  return function forYouScoreSorter(items = [], context = {}) {
+    if (!Array.isArray(items)) {
+      return [];
+    }
+    void context;
+    const copy = [...items];
+
+    const isMuted = (entry) =>
+      entry?.metadata?.moderation?.trustedMuted === true ||
+      entry?.video?.moderation?.trustedMuted === true;
+
+    const scoreOf = (entry) => {
+      const score = Number(entry?.metadata?.forYouScore);
+      return Number.isFinite(score) ? score : 0;
+    };
+
+    const timestampOf = (entry) => {
+      const video = entry?.video;
+      if (!video || typeof video !== "object") {
+        return Number.NEGATIVE_INFINITY;
+      }
+      const root = Number(video.rootCreatedAt);
+      if (Number.isFinite(root)) return Math.floor(root);
+      const created = Number(video.created_at);
+      return Number.isFinite(created) ? Math.floor(created) : Number.NEGATIVE_INFINITY;
+    };
+
+    copy.sort((a, b) => {
+      const aMuted = isMuted(a);
+      const bMuted = isMuted(b);
+      if (aMuted !== bMuted) {
+        return aMuted ? 1 : -1;
+      }
+      const scoreDiff = scoreOf(b) - scoreOf(a);
+      if (scoreDiff !== 0) {
+        return scoreDiff;
+      }
+      return timestampOf(b) - timestampOf(a);
+    });
+
+    return copy;
+  };
+}
+
 export function createChronologicalSorter({
   direction = "desc",
   postedAtResolver,