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/lookup/file.go

@@ -24,7 +24,7 @@ const quietTime = 2 * time.Second
 // FileParams are what OpenFile needs.
 type FileParams struct {
 	// Path is the lookup database, the IPinfo Lite file in its .mmdb form
-	// (SWW_LOOKUP_DB_PATH).
+	// (SWW_WAF_LOOKUP_DB_PATH).
 	Path string
 	// Now tells the time, normally time.Now.
 	Now func() time.Time
@@ -221,12 +221,12 @@ func (f *File) use(reader *maxminddb.Reader) {
 func read(path string) (*maxminddb.Reader, error) {
 	data, err := os.ReadFile(path) //nolint:gosec // the file the admin names
 	if err != nil {
-		return nil, fmt.Errorf("SWW_LOOKUP_DB_PATH cannot be read: %w", err)
+		return nil, fmt.Errorf("SWW_WAF_LOOKUP_DB_PATH cannot be read: %w", err)
 	}
 
 	reader, err := maxminddb.OpenBytes(data)
 	if err != nil {
-		return nil, fmt.Errorf("SWW_LOOKUP_DB_PATH %s is not a .mmdb file: %w", path, err)
+		return nil, fmt.Errorf("SWW_WAF_LOOKUP_DB_PATH %s is not a .mmdb file: %w", path, err)
 	}
 
 	return reader, nil

internal/lookup/file_internal_test.go

@@ -99,9 +99,9 @@ func TestFileThatCannotBeReadIsAnError(t *testing.T) {
 	writeFile(t, notDatabase, "not a lookup database\n")
 
 	for path, want := range map[string]string{
-		missing: "SWW_LOOKUP_DB_PATH cannot be read: open " + missing +
+		missing: "SWW_WAF_LOOKUP_DB_PATH cannot be read: open " + missing +
 			": no such file or directory",
-		notDatabase: "SWW_LOOKUP_DB_PATH " + notDatabase +
+		notDatabase: "SWW_WAF_LOOKUP_DB_PATH " + notDatabase +
 			" is not a .mmdb file: error opening database: invalid MaxMind DB file",
 	} {
 		_, err := OpenFile(FileParams{
@@ -216,7 +216,7 @@ func TestReplacementThatCannotBeReadLeavesTheFileInUseWithOneAlert(t *testing.T)
 			Reason: "the lookup database cannot be read, and the one read before stays in use",
 			Detail: map[string]any{
 				"file": path,
-				"error": "SWW_LOOKUP_DB_PATH " + path + " is not a .mmdb file: " +
+				"error": "SWW_WAF_LOOKUP_DB_PATH " + path + " is not a .mmdb file: " +
 					"error opening database: invalid MaxMind DB file",
 			},
 		})

internal/lookup/lookup.go

@@ -1,6 +1,6 @@
 // Package lookup looks up each client's AS number and country, through
 // the GeoJS web service or in the lookup database, the IPinfo Lite file
-// SWW_LOOKUP_DB_PATH names. GeoJS's answers are kept in memory, for at
+// SWW_WAF_LOOKUP_DB_PATH names. GeoJS's answers are kept in memory, for at
 // most 100,000 clients and for 7 days each, and are written to
 // lookups.json and read from it by the state package.
 package lookup
@@ -66,7 +66,7 @@ type Params struct {
 	URL string
 	// Timeout is how long a request waits for its client's first answer,
 	// and how long a request to GeoJS may take before it is abandoned
-	// (SWW_LOOKUP_TIMEOUT).
+	// (SWW_WAF_LOOKUP_TIMEOUT).
 	Timeout time.Duration
 	// Wait is true when a setting needs each request's answer before the
 	// request goes on. Otherwise no request waits for one.