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

@@ -27,20 +27,20 @@ main() {
 # give_state_dir_to_sww gives the state directory and every file in
 # it to the sww user, so that a volume mounted there needs no change
 # of owner; chown -R changes a symbolic link itself, never what it points
-# to. When SWW_STATE_DIR, in either form, cannot be read or is not the
+# to. When SWW_WAF_STATE_DIR, in either form, cannot be read or is not the
 # absolute path of a directory, no owner is changed, and waf starts and
 # stops with a message naming the setting. A change of owner that fails, as
 # on a volume mounted read-only, does not end the script either: waf
 # reports a directory it cannot write.
 give_state_dir_to_sww() {
     local dir
-    if dir="$(setting SWW_STATE_DIR /var/lib/sww)" &&
+    if dir="$(setting SWW_WAF_STATE_DIR /var/lib/sww)" &&
         [[ "$dir" == /* && -d "$dir" ]]; then
         chown -R sww:sww "$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, and gives it and every file in it to the sww user, as
 # give_state_dir_to_sww does the state directory. Unlike that one, it is
 # made when it is missing, since the cache files need no volume. As there,
@@ -48,7 +48,7 @@ give_state_dir_to_sww() {
 # 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
 }