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.

Model: opus-5-5

internal/waf/waf.go

@@ -212,8 +212,7 @@ type Result struct {
 // method, its URL with the query, and its headers, the Cookie header
 // without the cookies in cookiesNotRead, and on body, r's body as the
 // caller has it, as readBody reads it. It returns what it found, what it
-// read of body, which the app is still to be sent, and the error that
-// ended the reading early, if one did.
+// read of body, and the error that ended the reading early, if one did.
 func (c *CoreRuleSet) Inspect(
 	r *http.Request, client netip.Addr, body io.Reader,
 ) (Result, []byte, error) {