Discovery final review fixes: lean publish, robust scoring, cheap prune (BL-0051)

- Cache prune counts directory entries first and only reads files when over
  the cap; tests for cross-kind prune, schema-mismatch and corrupt entries.
- Scoring tolerates malformed manga.json and cached records (non-list tags,
  object or null relations, non-object items); a tag without a rank no longer
  passes the top-tag filter; authors without an integer AniList id are dropped.
- discovery.json publishes only candidates some feed shows; examined/clipped
  still describe the pool. Tests that asserted the published count equals the
  pool size now check the pool via candidatePool() and the published set
  against the feeds.
- The post-harvest rescore failure test now breaks discovery.json right before
  the publish (via a scraper stand-in) instead of relying on tags: 5, and a
  following successful harvest clears the stale lastError.
- Consent text names everything sent to AniList; paused label mentions admin
  harvests; the UI test asserts the XSS seed instead of skipping it.
- Slot-mix test proves the fresh/outside reservations matter.
- Docs: privacy note, fresh fallback reason, per-period cap, dry-run wording,
  published-candidate rule; plan/spec hygiene and spec status.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

discovery/cache.js

@@ -71,10 +71,14 @@ class DiscoveryCache {
     }
     return { files, bytes };
   }
-  // Oldest entries go first so the cache never grows past maxFiles.
+  // Oldest entries go first so the cache never grows past maxFiles. Every put() calls this, so
+  // under the cap it only counts directory entries; files are read only when something must go.
   prune() {
+    const byKind = KINDS.map(kind => [kind, this.files(kind)]);
+    if (byKind.reduce((sum, [, files]) => sum + files.length, 0) <= this.maxFiles) return;
     const all = [];
-    for (const kind of KINDS) for (const file of this.files(kind)) {
+    for (const [kind, files] of byKind) for (const file of files) {
+      // readFile drops corrupt and schema-mismatched files itself.
       const entry = this.readFile(file, kind);
       if (entry) all.push({ file, at: Date.parse(entry.fetchedAt) });
     }