build, deploy, inbound, dmarc, backup, e2e: cite the source of what they rely on (assumptions part C)

Comments only, no behaviour changed. Each main.cf/master.cf parameter the
build sets, the wrapper's and the reload hook's reliance on Postfix 3.7.11
(postfix-script, master.5, postconf.5, cleanup_init.c, smtpd_peer.c,
README_FILES), supervisor 4.2.5 (process.py, options.py, events.rst),
logrotate 3.21.0, OpenDKIM's config, Cyrus SASL's sasldb, rspamd 3.11.1
(milter_headers.lua, multimap, the map watcher), Docker Compose, CoreDNS
and certbot now say where that is written. Measurements already there stay
measurements ("date not recorded" where none was); hand-composed fixtures
say so.

Contradictions left for their own commits: C-P31 cleanup's size limit,
C-P42 master outside supervisor's signal, C-V5/V6 startsecs, C-V10,
C-S3/Q3 sasldb written in place, C-Q4/A1 certbot's symlinks, C-R7 rspamd
skips local clients but the signature routine does not, C-P8, C-R4, C-R12,
C-M7, C-E2, C-K8/K9, C-D1.

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

internal/dmarc/ingest.go

@@ -154,6 +154,10 @@ func extractAggregatePayload(raw []byte) ([]byte, error) {
 	return readEncodedBody(textproto.MIMEHeader(msg.Header), msg.Body)
 }
 
+// looksLikeAggregate takes a part by its file name or Content-Type. RFC 7489
+// § 7.2.1.1: the report is "application/gzip" if compressed and "text/xml"
+// otherwise, its name ending ".xml" or ".xml.gz"; zip is outside the RFC and
+// is what some reporters send (see decompress).
 func looksLikeAggregate(name string) bool {
 	name = strings.ToLower(name)
 	return strings.Contains(name, "xml") || strings.Contains(name, "gzip") || strings.Contains(name, "zip")