logtail, health, panel: cite the source of what they rely on (assumptions part A)

Comments only, no behaviour changed. Each place the log tailer, Health and
cmd/panel rely on another program now says where that is written, for the
version the image runs: Postfix 3.7.11 (log_adhoc(), msg_logger_print(),
smtpd_whatsup(), cleanup_milter.c, qmgr_active.c, postlogd.c, showq.c,
pipe.c), logrotate 3.21.0, supervisor 4.2.5, proc(5). Measurements stay
measurements and say where and when; test fixtures say whether they were
seen or composed.

Where the source contradicts the code the comment does not bless it but
names the register entry (A-8 expiry, A-12 the ISO stamp no Postfix writes,
A-15 the last recipient, A-21/A-23 sasl_username, A-33 postlogd's old
inode, A-38 a socket file is not a listener, A-65 the certificate served);
those are fixed in their own commits.

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

internal/health/health_test.go

@@ -33,7 +33,10 @@ func TestWorstPicksMostSevere(t *testing.T) {
 }
 
 func TestParseProcesses(t *testing.T) {
-	// Real supervisorctl output: column-aligned, one line per program.
+	// Real supervisorctl output: column-aligned, one line per program. Where
+	// and when it was seen is not recorded; its columns are those of
+	// supervisor 4.2.5 supervisorctl.py _show_statuses() and its FATAL text
+	// supervisor/process.py's spawnerr.
 	out := `opendkim                         RUNNING   pid 21, uptime 0:04:10
 panel                            RUNNING   pid 22, uptime 0:04:09
 postfix                          FATAL     Exited too quickly (process log may have details)
@@ -165,6 +168,7 @@ func writeCert(t *testing.T, path, cn string, validFor time.Duration) {
 }
 
 func TestLivenessFromParsedProcesses(t *testing.T) {
+	// Composed, in the columns of TestParseProcesses.
 	allRunning := `opendkim                         RUNNING   pid 21, uptime 0:04:10
 panel                            RUNNING   pid 22, uptime 0:04:09
 postfix                          RUNNING   pid 23, uptime 0:04:08
@@ -189,6 +193,9 @@ postfix                          FATAL     Exited too quickly
 	}
 }
 
+// Composed, after supervisor 4.2.5 rpcinterface.py _interpretProcessInfo()
+// (str() of a timedelta). "127:00:01" is not a form supervisor prints - it
+// only shows that the parser takes hours past 24.
 func TestUptime(t *testing.T) {
 	for detail, want := range map[string]time.Duration{
 		"pid 41, uptime 0:03:12":          3*time.Minute + 12*time.Second,