Rename the program to sww and its deciding daemon to discriminator

The program is now sww, built from cmd/sww, with two modes: sww rproxy and
sww discriminator. servewaf becomes discriminator everywhere it names that
daemon: the package (internal/discriminator), its types, functions, files, the
discriminator_line log field, and its docs and tests.

smallwebwaf is left only where sneak's directive allows it: the documents'
product name, the git.eeqj.de/sneak/smallwebwaf URLs, and the Go module path
sneak.berlin/go/smallwebwaf. Everywhere else a name containing it takes the sww
form: the package (internal/sww), metric names (sww_*), the X-Sww-* headers,
the /_sww/ admin endpoints, the OS user, and the state and rules directories.
The SWWAF_ environment variables take the SWW_ form.

No logic changes. make check passes.

Model: deepseek-v4-pro

internal/bans/snapshot_test.go

@@ -173,7 +173,7 @@ func TestPermanentBanStartedBeforeAnEndedOneRefuses(t *testing.T) {
 func TestNextBanWorkedOutFromTheBanThatEndedLast(t *testing.T) {
 	t.Parallel()
 
-	// A 9-hour ban smallwebwaf made, the third in a row, and an admin's
+	// A 9-hour ban sww made, the third in a row, and an admin's
 	// 1-hour ban added to bans.json over it, with no cause and no notes.
 	netblock := netip.MustParsePrefix("203.0.113.9/32")
 	nineHours := bans.Ban{