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

cmd/smallwebwaf/main.go

@@ -1,20 +0,0 @@
-// Command smallwebwaf is a web application firewall. `smallwebwaf rproxy` is
-// the reverse proxy in front of one app, which asks servewaf about each request.
-// `smallwebwaf servewaf` decides, for many sites, and keeps what lasts.
-// `smallwebwaf healthcheck` is the container's health check. Everything it does
-// is in internal/smallwebwaf.
-package main
-
-import (
-	"os"
-
-	"sneak.berlin/go/smallwebwaf/internal/smallwebwaf"
-)
-
-// Version is the version of the binary, set when it is built with
-// -ldflags "-X main.Version=...".
-var Version = "dev" //nolint:gochecknoglobals // the linker sets it
-
-func main() {
-	os.Exit(smallwebwaf.Main(Version))
-}

cmd/sww/main.go

@@ -0,0 +1,20 @@
+// Command sww is a web application firewall. `sww rproxy` is the reverse
+// proxy in front of one app, which asks discriminator about each request.
+// `sww discriminator` decides, for many sites, and keeps what lasts. `sww
+// healthcheck` is the container's health check. Everything it does is in
+// internal/sww.
+package main
+
+import (
+	"os"
+
+	"sneak.berlin/go/smallwebwaf/internal/sww"
+)
+
+// Version is the version of the binary, set when it is built with
+// -ldflags "-X main.Version=...".
+var Version = "dev" //nolint:gochecknoglobals // the linker sets it
+
+func main() {
+	os.Exit(sww.Main(Version))
+}