Fold sidecars (.nfo, .sfv, .nzb) apart from their upload into it

"Murdoch Mysteries S8D1 [00/80] - \"….nzb\"" beside its "[01/94]" upload
was a release of its own (23k sidecar-only releases on the corpus, 15k with
the poster's bigger release within 10 minutes). The settler queues small
settled releases (fold_candidates); the merger's third pass folds one whose
files are all sidecars into the poster's bigger release in the same group
within 10 minutes: the one sharing a 4+ letter word with its subject, else
the one under the same counter total, else none (via 'sidecar').

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

REBUILD.md

@@ -272,6 +272,15 @@ spot, a day after settling). Verdicts (`release_verdicts`, with the rule
 set's version) hide releases from search (`judged` shows them); a verdict
 whose rule no longer matches is taken back. Nothing is dropped yet.
 
+**Sidecars** (the merger's third pass). An upload's .nfo, .sfv or .nzb
+that came apart from it (another name, another counter: "[00/80] … .nzb"
+beside "[01/94] … .part01.rar") was a release of its own. The settler
+queues small settled releases (≤ 3 files, < 1 MB) in `fold_candidates`;
+one whose files are all sidecars joins the poster's bigger release in the
+same group posted within 10 minutes: the one sharing a word of 4+ letters
+with its subject, else the one under the same counter total, else none
+(`release_merges.via` 'sidecar').
+
 **Spots** (after voyager 1's D29; `lib/spotnet` ported as is). Two
 processes, one NNTP connection each: