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/mediawiki.conf

@@ -5,8 +5,8 @@
 # request, before the rules it switches off, so this file is loaded before the
 # Core Rule Set's rules. Each comment names a request a rule refused. An
 # exclusion on a field of a body applies only when the query has no parameter of
-# that name, so it matters only while SWW_WAF_BODY_LIMIT is set. MediaWiki's
-# paths are matched at the site root and under /w/.
+# that name, so it matters only while SWW_WAF_CORE_RULE_SET_BODY_LIMIT is set.
+# MediaWiki's paths are matched at the site root and under /w/.
 #
 # WordPress serves /index.php too. So /index.php counts as MediaWiki's only
 # with a page title, in the query or after the path:
@@ -22,7 +22,7 @@
 #   932260: python3
 
 # Every rule below is skipped unless Inspect has set tx.app_mediawiki. It sets
-# it while SWW_APPS is unset, or lists mediawiki for the request's hostname.
+# it while SWW_WAF_APPS is unset, or lists mediawiki for the request's hostname.
 # The skip reaches only phase 1, so a rule of a later phase must check
 # tx.app_mediawiki itself.
 SecRule &TX:app_mediawiki "@eq 0" \