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)

script/example-app

@@ -17,10 +17,10 @@
 #   - that a new waf container on the same volume still refuses the banned
 #     client;
 #   - that a waf container with its state files on a new volume mounted at
-#     the directory SWW_STATE_DIR_FILE names becomes healthy;
-#   - that one whose SWW_STATE_DIR does not exist logs waf's message
+#     the directory SWW_WAF_STATE_DIR_FILE names becomes healthy;
+#   - that one whose SWW_WAF_STATE_DIR does not exist logs waf's message
 #     about it.
-# waf runs with SWW_LOOKUP_SOURCE=off, so that no address is sent to
+# waf runs with SWW_WAF_LOOKUP_SOURCE=off, so that no address is sent to
 # GeoJS. The containers, the network, the volumes and both images are removed
 # however the script ends. Building the app needs network access, for nixpkgs'
 # binary cache. script/check does not run this.
@@ -38,7 +38,7 @@ NETWORK="$NAME"
 APP="$NAME-app-container"
 WAF="$NAME-waf"
 VOLUME="$NAME-state"
-# The volumes of the container whose state directory SWW_STATE_DIR_FILE
+# The volumes of the container whose state directory SWW_WAF_STATE_DIR_FILE
 # names: its state files, and the file that names their directory.
 MOVED_VOLUME="$NAME-moved-state"
 SETTINGS_VOLUME="$NAME-settings"
@@ -95,8 +95,8 @@ start_waf() {
     docker run --detach --name "$WAF" --network "$NETWORK" \
         --volume "$VOLUME:/var/lib/sww" \
         --env SWW_COMMAND=waf \
-        --env SWW_RATE_LIMIT_PER_MINUTE=1 \
-        --env SWW_LOOKUP_SOURCE=off \
+        --env SWW_WAF_RATE_LIMIT_PER_MINUTE=1 \
+        --env SWW_WAF_LOOKUP_SOURCE=off \
         "$IMAGE" >/dev/null
     wait_for "waf's health check did not pass" healthy "$WAF"
 }
@@ -105,14 +105,14 @@ start_waf() {
 # healthy.
 start_app() {
     docker run --detach --name "$APP" --network "$NETWORK" --publish 127.0.0.1::8080 \
-        --env SWRP_WAF_BACKEND="http://$WAF:8080" \
+        --env SWW_RPROXY_WAF_BACKEND="http://$WAF:8080" \
         "$APP_IMAGE" >/dev/null
     wait_for "the app's health check did not pass" healthy "$APP"
     address="$(docker port "$APP" 8080/tcp)"
 }
 
 # start_moved_waf: run waf with the state files on a new volume at
-# /srv/state, which SWW_STATE_DIR_FILE names in a file only the sww
+# /srv/state, which SWW_WAF_STATE_DIR_FILE names in a file only the sww
 # user can read, as under "Settings given as files" in docs/settings.md, and
 # wait until it is healthy. waf can write the new volume only once the run
 # script has given it to that user.
@@ -127,8 +127,8 @@ start_moved_waf() {
         --volume "$MOVED_VOLUME:/srv/state" \
         --volume "$SETTINGS_VOLUME:/etc/sww/settings:ro" \
         --env SWW_COMMAND=waf \
-        --env SWW_STATE_DIR_FILE=/etc/sww/settings/state-dir \
-        --env SWW_LOOKUP_SOURCE=off \
+        --env SWW_WAF_STATE_DIR_FILE=/etc/sww/settings/state-dir \
+        --env SWW_WAF_LOOKUP_SOURCE=off \
         "$IMAGE" >/dev/null
     wait_for "waf's health check did not pass" healthy "$WAF"
 }
@@ -141,7 +141,7 @@ status_from() {
         --max-time 10 --header "X-Forwarded-For: $1" "http://$address$2" || true
 }
 
-# refused: a request to the container gets 403, SWW_BAN_RESPONSE's
+# refused: a request to the container gets 403, SWW_WAF_BAN_RESPONSE's
 # default.
 refused() {
     code="$(curl --silent --output /dev/null --write-out '%{http_code}' \
@@ -208,7 +208,7 @@ main() {
     wait_for "waf did not stop in order" logged "$WAF" '"msg":"stopped"'
     [ "$(status_from 203.0.113.9 /)" = 200 ] ||
         fail "with waf stopped, the app did not answer through rproxy"
-    wait_for "rproxy logged no request SWRP_DEFAULT_DISPOSITION decided" \
+    wait_for "rproxy logged no request SWW_RPROXY_DEFAULT_DISPOSITION decided" \
         logged "$APP" '"default_disposition":true'
     docker exec "$APP" /usr/local/bin/sww healthcheck ||
         fail "with waf stopped, the app's health check failed"
@@ -243,16 +243,16 @@ main() {
     docker rm --force "$WAF" >/dev/null
     start_moved_waf
     echo "example-app: the run script gives the state files' directory named" \
-        "by SWW_STATE_DIR_FILE to the sww user"
+        "by SWW_WAF_STATE_DIR_FILE to the sww user"
 
     docker rm --force "$WAF" >/dev/null
     docker run --detach --name "$WAF" --network "$NETWORK" \
         --env SWW_COMMAND=waf \
-        --env SWW_STATE_DIR=/srv/missing \
-        --env SWW_LOOKUP_SOURCE=off \
+        --env SWW_WAF_STATE_DIR=/srv/missing \
+        --env SWW_WAF_LOOKUP_SOURCE=off \
         "$IMAGE" >/dev/null
     wait_for "waf did not report the missing state directory" \
-        logged "$WAF" "SWW_STATE_DIR cannot be written"
+        logged "$WAF" "SWW_WAF_STATE_DIR cannot be written"
     echo "example-app: waf reports a state directory that does not exist"
 }