Rename the program to sww and its deciding daemon to discriminator (closes #218)

The program is now sww, built from cmd/sww, with two modes: sww rproxy and
sww discriminator. servewaf becomes discriminator everywhere it names that
daemon: the package (internal/discriminator), its types, functions, files, the
discriminator_line log field, and its docs and tests.

smallwebwaf is left only where sneak's directive allows it: the documents'
product name, the git.eeqj.de/sneak/smallwebwaf URLs, and the Go module path
sneak.berlin/go/smallwebwaf. Everywhere else a name containing it takes the sww
form: the package (internal/sww), metric names (sww_*), the X-Sww-* headers,
the /_sww/ admin endpoints, the OS user, and the state and rules directories.
The SWWAF_ environment variables take the SWW_ form.

No logic changes. make check passes.

Model: deepseek-v4-pro

share/sww.run

@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# runit's run script for sww, run again whenever sww
+# exits; the wait spaces out the restarts. SWW_COMMAND names the
+# command to run: rproxy when it is unset or empty, or discriminator. With any
+# other value the script starts nothing and stops with a message naming it.
+# exec, so that the signal `sv stop` sends reaches sww itself.
+main() {
+    sleep 1
+    local command="${SWW_COMMAND:-rproxy}"
+    case "$command" in
+        rproxy) ;;
+        discriminator) give_state_dir_to_sww ;;
+        *)
+            printf 'SWW_COMMAND: "%s" is not rproxy or discriminator\n' \
+                "$command" >&2
+            exit 1
+            ;;
+    esac
+    exec chpst -u sww:sww /usr/local/bin/sww "$command"
+}
+
+# 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
+# absolute path of a directory, no owner is changed, and discriminator 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: discriminator
+# reports a directory it cannot write.
+give_state_dir_to_sww() {
+    local dir
+    if dir="$(state_dir)" && [[ "$dir" == /* && -d "$dir" ]]; then
+        chown -R sww:sww "$dir" || true
+    fi
+}
+
+# state_dir prints SWW_STATE_DIR, /var/lib/sww when it is unset,
+# or what is in the file SWW_STATE_DIR_FILE names, less every newline at
+# its end. It fails when both are set or the file cannot be read.
+state_dir() {
+    if [[ ! -v SWW_STATE_DIR_FILE ]]; then
+        printf '%s\n' "${SWW_STATE_DIR-/var/lib/sww}"
+    elif [[ ! -v SWW_STATE_DIR ]]; then
+        cat -- "$SWW_STATE_DIR_FILE" 2>/dev/null
+    else
+        return 1
+    fi
+}
+
+main "$@"