Rename discriminator to waf everywhere (closes #312)

The command is now `sww waf`, and the package is `internal/waf`. Types,
functions, files, tests, comments, docs, the Dockerfile, the runit
script, `script/`, compose examples, the log field `waf_line` and the
`X-From-Waf` test header follow. No behaviour changes, and no setting
changes name: rproxy already finds the waf through `SWRP_WAF_BACKEND`.

Done with one `sed -i` (Discriminator and DISCRIMINATOR to WAF,
discriminator to waf) over the files `git grep -i discriminator`
listed, as sneak allowed for this rename, then `git mv` for the
package and files. By hand afterwards: the header's spelling, which
the linter requires, and the padding after `waf` in `sww`'s usage
text.

Model: opus-5-5

internal/config/rproxy.go

@@ -22,12 +22,12 @@ type RProxy struct {
 	// TrustedProxies are the netblocks whose X-Forwarded-For is believed
 	// (SWRP_TRUSTED_PROXIES).
 	TrustedProxies []netip.Prefix
-	// WAFBackend is discriminator's URL (SWRP_WAF_BACKEND).
+	// WAFBackend is waf's URL (SWRP_WAF_BACKEND).
 	WAFBackend *url.URL
-	// Timeout is how long rproxy waits for discriminator's answer to a question,
+	// Timeout is how long rproxy waits for waf's answer to a question,
 	// and to a report (SWRP_TIMEOUT_MS). It cannot be off.
 	Timeout time.Duration
-	// DefaultDisposition is what is done with a request when discriminator cannot be
+	// DefaultDisposition is what is done with a request when waf cannot be
 	// connected to, does not answer at all, or does not answer within Timeout:
 	// allow or deny (SWRP_DEFAULT_DISPOSITION).
 	DefaultDisposition string
@@ -50,7 +50,7 @@ type RProxy struct {
 
 var (
 	errNeedsWAFBackend = errors.New(
-		"is required: it is discriminator's URL, such as http://discriminator:8080")
+		"is required: it is waf's URL, such as http://waf:8080")
 	errNotDisposition  = errors.New("is not allow or deny")
 	errNotMilliseconds = errors.New(
 		"is not a whole number of milliseconds above zero, such as 2000")
@@ -124,7 +124,7 @@ func (c *RProxy) LogValue() slog.Value {
 	return slog.GroupValue(c.settings...)
 }
 
-// wafBackend reads the setting that is discriminator's URL, which must be set.
+// wafBackend reads the setting that is waf's URL, which must be set.
 func (e *environment) wafBackend(name string) *url.URL {
 	value := e.value(name, "")
 	if value == "" {
@@ -139,7 +139,7 @@ func (e *environment) wafBackend(name string) *url.URL {
 	return backend
 }
 
-// disposition reads the setting that is what is done with a request when discriminator
+// disposition reads the setting that is what is done with a request when waf
 // cannot be connected to, does not answer at all, or does not answer in time:
 // allow or deny.
 func (e *environment) disposition(name, defaultValue string) string {