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/coreruleset/forgejo_test.go

@@ -8,10 +8,10 @@ import (
 	"sneak.berlin/go/smallwebwaf/internal/coreruleset"
 )
 
-// forgejo is Forgejo's name in SWW_APPS.
+// forgejo is Forgejo's name in SWW_WAF_APPS.
 const forgejo = "forgejo"
 
-// forgejoHost is the hostname of the tests of SWW_APPS that serves Forgejo.
+// forgejoHost is the hostname of the tests of SWW_WAF_APPS that serves Forgejo.
 const forgejoHost = "code.example"
 
 func TestForgejoFixesApplyOnlyToAHostnameThatServesForgejo(t *testing.T) {
@@ -91,7 +91,7 @@ var forgejoAttacks = []string{
 func TestForgejoAttacksAreRefusedInItsSearches(t *testing.T) {
 	t.Parallel()
 
-	const threshold = 5 // SWW_WAF_ANOMALY_THRESHOLD's default
+	const threshold = 5 // SWW_WAF_CORE_RULE_SET_ANOMALY_THRESHOLD's default
 
 	defaults, bodies := atDefaults(t), readingBodies(t)
 
@@ -113,7 +113,7 @@ func TestForgejoAttacksAreRefusedInItsSearches(t *testing.T) {
 func TestForgejoExclusionsAreNarrow(t *testing.T) {
 	t.Parallel()
 
-	const threshold = 5 // SWW_WAF_ANOMALY_THRESHOLD's default
+	const threshold = 5 // SWW_WAF_CORE_RULE_SET_ANOMALY_THRESHOLD's default
 
 	crs := atDefaults(t)