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/reputation/abuseipdb.go

@@ -58,17 +58,17 @@ type Checks struct {
 // AbuseIPDBParams are what NewAbuseIPDB needs.
 type AbuseIPDBParams struct {
 	// URL is where clients are checked, normally AbuseIPDBURL, with Key,
-	// the account's key (SWW_ABUSEIPDB_KEY).
+	// the account's key (SWW_WAF_ABUSEIPDB_KEY).
 	URL string
 	Key string
-	// MinScore is the least score that is a hit (SWW_ABUSEIPDB_MIN_SCORE),
+	// MinScore is the least score that is a hit (SWW_WAF_ABUSEIPDB_MIN_SCORE),
 	// and DailyBudget the most checks made in a day, in UTC
-	// (SWW_ABUSEIPDB_DAILY_BUDGET).
+	// (SWW_WAF_ABUSEIPDB_DAILY_BUDGET).
 	MinScore    int64
 	DailyBudget int
 	// CacheTTL is how long a score is used after it was fetched
-	// (SWW_REPUTATION_CACHE_TTL), and Timeout how long a check may take
-	// (SWW_REPUTATION_TIMEOUT).
+	// (SWW_WAF_REPUTATION_CACHE_TTL), and Timeout how long a check may take
+	// (SWW_WAF_REPUTATION_TIMEOUT).
 	CacheTTL time.Duration
 	Timeout  time.Duration
 	// Now tells the time, normally time.Now in UTC.