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>

build/postfix-cert-reload.sh

@@ -11,6 +11,11 @@
 # copies - not the mounted files, which a renewer may be rewriting - are a
 # certificate and the key that belongs to it, renames both over the targets
 # and reloads Postfix. When nothing changed it does nothing.
+# (Postfix 3.7.11: smtpd loads the certificate in pre_jail_init(), once per
+# process, src/smtpd/smtpd.c; "postfix reload" is SIGHUP to master,
+# conf/postfix-script, after which the old smtpd processes exit on the closed
+# status pipe, src/master/master_conf.c, master_config() ->
+# master_restart_service(), and new ones load the files again.)
 #
 # Runs under supervisord as root. It sleeps first: at container start the
 # wrapper is still bringing Postfix up. It never exits non-zero, so a failure