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)

share/sww.run

@@ -24,7 +24,7 @@ main() {
     exec chpst -u sww:sww /usr/local/bin/sww "$command"
 }
 
-# make_state_dir_for_sww makes the state directory, SWW_STATE_DIR in
+# make_state_dir_for_sww makes the state directory, SWW_WAF_STATE_DIR in
 # either form, when it is missing, gives it and every file in it to the
 # sww user, and sets its mode to 0700. So a volume mounted there needs no
 # change of owner; chown -R changes a symbolic link itself, never what it
@@ -34,20 +34,20 @@ main() {
 # end the script either: waf reports a directory it cannot write.
 make_state_dir_for_sww() {
     local dir
-    if dir="$(setting SWW_STATE_DIR /var/lib/sww)" && [[ "$dir" == /* ]]; then
+    if dir="$(setting SWW_WAF_STATE_DIR /var/lib/sww)" && [[ "$dir" == /* ]]; then
         { mkdir -p -- "$dir" && chown -R sww:sww "$dir" &&
             chmod 0700 "$dir"; } || true
     fi
 }
 
-# make_cache_dir_for_sww makes the cache directory, SWW_CACHE_DIR in
+# make_cache_dir_for_sww makes the cache directory, SWW_WAF_CACHE_DIR in
 # either form, when it is missing, and gives it and every file in it to
 # the sww user. As for the state directory, a setting that cannot be read
 # or is not an absolute path changes nothing, and a failure does not end
 # the script.
 make_cache_dir_for_sww() {
     local dir
-    if dir="$(setting SWW_CACHE_DIR /var/cache/sww)" && [[ "$dir" == /* ]]; then
+    if dir="$(setting SWW_WAF_CACHE_DIR /var/cache/sww)" && [[ "$dir" == /* ]]; then
         { mkdir -p -- "$dir" && chown -R sww:sww "$dir"; } || true
     fi
 }