Lone articles under scrambled names are per-article; inactive groups get no corpus fill

One article of a multi-part file under a name like "nYDeXeF49dieZ1J7flK-JFzZ3j.ZEDsr" or
"bslXlwgPiqZadhRa" (a random subject and poster per article, with fake counters) was a release:
looksRandom misses these names for their separators. 160k of alt.binaries.storage's 162k
non-Bob releases, and about 60% of all single-article releases in a 2% sample.

looks_scrambled / isScrambledFile: at least half the stem's letters and digits in tokens of 5+
that switch case or letter/digit 3 times or more (93% of the storage spam). Used for lone
articles given up before the block's end only; at the end the strict looksRandom stays, as the
rest of such a file can be in the next block. The namer's re-index (partialFiles) does the same.

The prefetcher's corpus fill skips groups that aren't active.

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

app/services/prefetcher.ts

@@ -561,6 +561,8 @@ export class Prefetcher {
     const groups = new Map<string, number>()
     const candidates = await rows(db.query())
       .where('r.capture', true)
+      // A group taken off the list (groups.active) isn't worth the connections.
+      .where('g.active', true)
       .whereNull('r.stored_at')
       .where((q: any) =>
         q