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/forgejo.conf

@@ -6,7 +6,7 @@
 # rules. Each comment names a request the rule refused.
 
 # Every rule below is skipped unless Inspect has set tx.app_forgejo. It sets it
-# while SWW_APPS is unset, or lists forgejo for the request's hostname.
+# while SWW_WAF_APPS is unset, or lists forgejo for the request's hostname.
 # The skip reaches only phase 1, so a rule of a later phase must check
 # tx.app_forgejo itself.
 SecRule &TX:app_forgejo "@eq 0" \
@@ -132,8 +132,8 @@ SecRule REQUEST_FILENAME "@streq /admin/repos" \
 # They skip these rules:
 #   932120: fix-powershell-module
 #   932260: feat/docker-support
-# They are read only while SWW_WAF_BODY_LIMIT is set, and skip nothing when the
-# query has a parameter of the same name.
+# They are read only while SWW_WAF_CORE_RULE_SET_BODY_LIMIT is set, and skip
+# nothing when the query has a parameter of the same name.
 SecRule REQUEST_FILENAME "@rx ^/[^/]+/[^/]+/settings/rename_branch$" \
     "id:900666,phase:1,pass,nolog,chain"
     SecRule &ARGS_GET:/^(?:from|to)$/ "@eq 0" \