Read every setting through viper and rename the settings (closes #211)

Every setting of waf and rproxy is read through viper, in place of the
os.LookupEnv function Main passed down. NewViper turns AutomaticEnv and
AllowEmptyEnv on, so a setting that is set but empty reads as set. A
setting may also be given as a file, the _FILE form, which rproxy's
settings now have too; rproxy still writes nothing to disk.

The settings are renamed: waf's take the prefix SWW_WAF_, rproxy's take
SWW_RPROXY_, and the shared SWW_COMMAND keeps SWW_. The Core Rule Set's
settings take SWW_WAF_CORE_RULE_SET_ rather than SWW_WAF_WAF_.

Model: deepseek-v4-pro (first version); opus-5-5 (rework)

internal/waf/waf_test.go

@@ -39,7 +39,7 @@ const (
 	// reportBodyLimit is the longest body SPEC.md lets a report have.
 	reportBodyLimit = 1 << 20
 	// anomalyClientPerMinute is the anomaly threshold these tests set.
-	anomalyClientPerMinute = "SWW_ANOMALY_CLIENT_REQUESTS_PER_MINUTE"
+	anomalyClientPerMinute = "SWW_WAF_ANOMALY_CLIENT_REQUESTS_PER_MINUTE"
 )
 
 // The fields of a report, as "waf" in SPEC.md names them.
@@ -181,7 +181,7 @@ func (s *WAF) history() ratelimit.History {
 }
 
 // metrics returns what the metrics endpoint answers, for a server started with
-// the token as SWW_METRICS_TOKEN.
+// the token as SWW_WAF_METRICS_TOKEN.
 func (s *WAF) metrics() string {
 	s.t.Helper()
 
@@ -1702,7 +1702,7 @@ func TestALargeBodyAnnouncedAndLongHeadersAreNoReasonToRefuse(t *testing.T) {
 func TestLogLevelHoldsBackNoRequestLine(t *testing.T) {
 	t.Parallel()
 
-	s := startWAF(t, "", map[string]string{"SWW_LOG_LEVEL": "error"})
+	s := startWAF(t, "", map[string]string{"SWW_WAF_LOG_LEVEL": "error"})
 
 	// A refused question would write a process warning, held back at error.
 	req := s.question(siteA, client, "/")