Every time in UTC, and every day as YYYY-MM-DD (closes #313)

AbuseIPDB's daily count keeps its day as a civil.Date, taken from the UTC
clock and written to reputation.json as "YYYY-MM-DD"; it was a time.Time
at midnight. A test runs sww discriminator with TZ 14 hours ahead of UTC
and checks the process line, the request line and clients.json are in
UTC. SPEC.md states the rule near its start; AGENTS.md makes it an iron
rule.

Model: opus-5-5

internal/lookup/file.go

@@ -26,7 +26,7 @@ type FileParams struct {
 	// Path is the lookup database, the IPinfo Lite file in its .mmdb form
 	// (SWW_LOOKUP_DB_PATH).
 	Path string
-	// Now tells the time, normally time.Now.
+	// Now tells the time, normally time.Now in UTC.
 	Now func() time.Time
 	// ProcessLog receives each reading of the file, and why a replacement
 	// of it cannot be read.

internal/lookup/lookup.go

@@ -74,7 +74,7 @@ type Params struct {
 	// Answered, unless nil, is given each answer GeoJS gives, once it is
 	// kept.
 	Answered func(Answer)
-	// Now tells the time, normally time.Now.
+	// Now tells the time, normally time.Now in UTC.
 	Now func() time.Time
 	// ProcessLog receives GeoJS's failures.
 	ProcessLog *slog.Logger