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/rules/rules.go

@@ -1,5 +1,5 @@
 // Package rules reads the rule files: the plain text files in
-// SWW_RULES_DIR, one rule to a line, that each request is checked
+// SWW_WAF_RULES_DIR, one rule to a line, that each request is checked
 // against, as the "Rule files" section of SPEC.md describes. They are read
 // at start, and again once the directory has had no change for a short
 // time after one is edited, added or removed.
@@ -40,7 +40,7 @@ const (
 // extension ends the name of every rule file.
 const extension = ".rules"
 
-// quietTime is how long SWW_RULES_DIR must go without a change before
+// quietTime is how long SWW_WAF_RULES_DIR must go without a change before
 // the rule files are read again, so that a file still being written, such
 // as one saved in place, appended to or copied in with scp, is read only
 // once whole.
@@ -100,9 +100,9 @@ type Rule struct {
 
 // Params are what Load needs.
 type Params struct {
-	// Dir is the directory of the rule files (SWW_RULES_DIR).
+	// Dir is the directory of the rule files (SWW_WAF_RULES_DIR).
 	Dir string
-	// Enabled is SWW_RULES_ENABLED: while it is false, no file is read
+	// Enabled is SWW_WAF_RULES_ENABLED: while it is false, no file is read
 	// and no rule loaded.
 	Enabled bool
 	// ProcessLog receives how many rules were read, and the error in a
@@ -271,7 +271,7 @@ func (f *Files) logRead(count int) {
 func read(dir string) ([]Rule, string, error) {
 	entries, err := os.ReadDir(dir)
 	if err != nil {
-		return nil, dir, fmt.Errorf("SWW_RULES_DIR cannot be read: %w", err)
+		return nil, dir, fmt.Errorf("SWW_WAF_RULES_DIR cannot be read: %w", err)
 	}
 
 	var rules []Rule
@@ -299,7 +299,7 @@ func read(dir string) ([]Rule, string, error) {
 // readFile appends the rules of the rule file at path to rules. places
 // are where each id read so far is, and gain those of the file.
 func readFile(path string, rules []Rule, places map[string]string) ([]Rule, error) {
-	data, err := os.ReadFile(path) //nolint:gosec // a rule file, in SWW_RULES_DIR
+	data, err := os.ReadFile(path) //nolint:gosec // a rule file, in SWW_WAF_RULES_DIR
 	if err != nil {
 		return nil, err
 	}