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

Every setting of discriminator 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. Discriminator'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_.
Every place a name appeared changed: the code, the viper keys, tests,
documents, examples, the README's settings table and the image files.

Model: deepseek-v4-pro

internal/discriminator/coreruleset.go

@@ -10,10 +10,11 @@ import (
 )
 
 // checkCoreRuleSet inspects the request with the Core Rule Set, unless
-// SWW_WAF_MODE is off or SWW_WAF_EXEMPT_PATHS exempts its path, as
+// SWW_WAF_CORE_RULE_SET_MODE is off or SWW_WAF_CORE_RULE_SET_EXEMPT_PATHS exempts its
+// path, as
 // pathExempt decides, and notes the rules it matched and its score in the
 // log line, and the rules in the metrics. A score at or over
-// SWW_WAF_ANOMALY_THRESHOLD is a match: it raises the waf_block alert,
+// SWW_WAF_CORE_RULE_SET_ANOMALY_THRESHOLD is a match: it raises the waf_block alert,
 // and in block mode refuses the request, which is an offence its client's
 // history counts, and so returns ActionWAFBlocked. It returns "" for a
 // request it does not refuse.
@@ -55,7 +56,7 @@ func (rq *request) checkCoreRuleSet() string {
 }
 
 // alertWAFBlock raises the waf_block alert for the request, which the Core
-// Rule Set scored at result, at or over SWW_WAF_ANOMALY_THRESHOLD. Its
+// Rule Set scored at result, at or over SWW_WAF_CORE_RULE_SET_ANOMALY_THRESHOLD. Its
 // detail gives the rule ids, the score, the method and the path with the
 // query, and, for a request that is not refused for it, the mode: detect,
 // or observe in observe mode.
@@ -82,7 +83,8 @@ func (rq *request) alertWAFBlock(result waf.Result) {
 		ASN:      rq.line.ASN,
 		ASName:   rq.line.ASName,
 		Country:  rq.line.Country,
-		Reason:   "scored by the Core Rule Set at or over SWW_WAF_ANOMALY_THRESHOLD",
-		Detail:   detail,
+		Reason: "scored by the Core Rule Set at or over " +
+			"SWW_WAF_CORE_RULE_SET_ANOMALY_THRESHOLD",
+		Detail: detail,
 	})
 }