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/sink/Dockerfile

@@ -21,6 +21,9 @@ WORKDIR /mail
 # smtp-sink refuses to run as root without an explicit -u to switch to after
 # binding — "-u root" satisfies that check while staying root throughout,
 # which is fine here: throwaway container, isolated e2e network, never
-# exposed.
+# exposed. (Postfix 3.7.11, src/smtpstone/smtp-sink.c: -d "Dump each mail
+# transaction to a single-message file" named by the template plus "a
+# pseudo-random hexadecimal number"; main(): "-u option is required if running
+# as root".)
 ENTRYPOINT ["/usr/sbin/smtp-sink"]
 CMD ["-u", "root", "-d", "/mail/%Y%m%d%H%M%S.", "0.0.0.0:25", "100"]