rproxy and servewaf replace the one-process smallwebwaf (closes #172, closes #165)

`smallwebwaf` with no command now prints the commands and exits with status 2.
The image runs rproxy, or servewaf with SMALLWEBWAF_COMMAND=servewaf. The
passing-on code, its settings and its log fields and metric go. internal/proxy
keeps the checks, answers, reports and own endpoints; its tests run through the
real rproxy. The documents describe the pair.

Judgement call: clients.json keeps token_refused, since state files refuse unknown fields.
Deviation: script/gitea-requests sets SWWAF_LOG_REQUEST_HEADERS, to label requests.
Partially verified: make example-app and make gitea-requests never built the image, as Ubuntu's snapshot service answered 5xx.

Model: opus-5-5

internal/proxy/anomaly_test.go

@@ -117,6 +117,7 @@ func TestEachScopeAndWindowOverItsThresholdAlertsOncePerCooldown(t *testing.T) {
 					Instance: alertInstance,
 					Time:     start,
 					Event:    alerts.EventAnomaly,
+					Host:     appHost,
 					Client:   netip.MustParseAddr(client),
 					Netblock: scope.netblock,
 					ASN:      asnDE,