store, web: cite the source of what they rely on (assumptions part D)

Comments only, no behaviour changed. modernc.org/sqlite v1.60.1 (the
_pragma list on every connection, busy_timeout first; extended result
codes; a deferred BEGIN; multi-statement Exec) and SQLite 3.53.4's
documentation (transactions, WAL, foreign keys, NOCASE, upsert, julianday,
partial indexes); htmx 2.0.4 src/htmx.js; the Fetch and HTML standards for
Sec-Fetch-Site, Origin, SameSite, __Host-, CSP and defer order; Go's
html/template. Comments the source contradicts are corrected - the driver
does not serialise writes (SetMaxOpenConns(1) does), htmx:load fires per
swapped element, no-store does not keep a page out of history.

Left for their own commits: D-S3 a migration two processes can both run,
D-S20 recipient case, D-B3 Origin: null under Referrer-Policy: no-referrer,
D-H5/H6/H7/H9 (audit M11, stage 4).

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

internal/store/sendloglines.go

@@ -43,7 +43,12 @@ func cutSendLogLine(line string) string {
 // wrote. The tailer calls it with what it read in one pass over the log,
 // whether or not send-log rows exist for the queue ids yet: a commit per line
 // would be a disk sync per line, on the one connection the journal milter
-// writes through.
+// writes through. SQLite 3.53.4 as modernc builds it keeps synchronous at FULL
+// (SQLITE_DEFAULT_WAL_SYNCHRONOUS 2), and in WAL mode FULL syncs the WAL at
+// every commit (https://sqlite.org/wal.html § 2.3, pragma.html#pragma_synchronous).
+// The first statement stepped is an INSERT, a write (see UpdateStatus):
+// tx.Prepare leaves no transaction open (prepare.c sqlite3InitOne() commits
+// the read it opens to load the schema).
 //
 // With once set, a line is written only if the same line is not there already
 // under its queue id. That is for the lines the tailer reads again after an