Rename the program to sww and its deciding daemon to discriminator (closes #218)

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/rules/rules_test.go

@@ -298,7 +298,7 @@ func TestDirectoryThatDoesNotExistStopsTheStart(t *testing.T) {
 
 	dir := filepath.Join(t.TempDir(), "rules.d")
 
-	wantRefused(t, dir, "SWWAF_RULES_DIR cannot be read: open "+dir+
+	wantRefused(t, dir, "SWW_RULES_DIR cannot be read: open "+dir+
 		": no such file or directory")
 }
 
@@ -321,7 +321,7 @@ func TestEmptyDirectoryLoadsNoRulesAndSaysSo(t *testing.T) {
 func TestRuleFilesOffReadNothing(t *testing.T) {
 	t.Parallel()
 
-	// SWWAF_RULES_DIR does not exist, which would stop the start.
+	// SWW_RULES_DIR does not exist, which would stop the start.
 	params, _ := newParams(filepath.Join(t.TempDir(), "rules.d"))
 	params.Enabled = false
 
@@ -601,7 +601,7 @@ func wantRefused(t *testing.T, dir, want string) {
 }
 
 // get returns a GET request for target, a path and an optional query, as
-// smallwebwaf's server reads it, without a user agent.
+// sww's server reads it, without a user agent.
 func get(t *testing.T, target string) *http.Request {
 	t.Helper()