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>

test/e2e/mail_helpers.go

@@ -69,6 +69,8 @@ func verifyDKIM(raw []byte, domain string) error {
 // observed for a just-made connection (needed to configure a level-2 rate
 // limit's allowed-IPs list — the address a host-published port is seen as
 // inside the container depends on Docker's NAT and isn't worth hard-coding).
+// Postfix 3.7.11, src/smtpd/smtpd.c, smtpd_service(): msg_info("connect from
+// %s", namaddr), namaddr being "name[addr]".
 var connectFromPattern = regexp.MustCompile(`connect from [^\[]*\[([0-9a-fA-F.:]+)\]`)
 
 // lastSMTPClientIP reads mail.log inside the selfpost container and returns