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/web/auth/middleware.go

@@ -34,6 +34,10 @@ func (m *Module) RequireAuth(next http.Handler) http.Handler {
 	})
 }
 
+// isSessionActivity: a GET from htmx is a background poll - every panel hx-get
+// is a load or a poll - and does not renew the session. htmx 2.0.4, src/htmx.js
+// getHeaders(): every request it issues carries HX-Request: true (and
+// loadHistoryFromServer() sets it too).
 func isSessionActivity(r *http.Request) bool {
 	return !(r.Method == http.MethodGet && r.Header.Get("HX-Request") != "")
 }