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/ratelimit/ratelimit.go

@@ -92,10 +92,9 @@ type History struct {
 	ASName   string    `json:"as_name,omitempty"`
 	Country  string    `json:"country,omitempty"`
 	LookedUp time.Time `json:"looked_up,omitzero"`
-	// Requests are all the client's requests: Forwarded those passed to
-	// the app, Refused those refused before anything reached it, a 401 at
-	// smallwebwaf's own endpoints included, and neither the others
-	// smallwebwaf answered there.
+	// Requests are all the client's requests: Forwarded those servewaf allowed,
+	// Refused those it refused, and neither those for a path under
+	// /_smallwebwaf/.
 	Requests  int64 `json:"requests"`
 	Forwarded int64 `json:"forwarded"`
 	Refused   int64 `json:"refused"`
@@ -124,21 +123,20 @@ type Offences struct {
 	// Limit is its requests that broke a rate limit, a byte limit or the
 	// error burst, Attack those that were a clear sign of attack, a match
 	// of a ban rule or a request for a trap path, RuleBlocked those a block
-	// rule refused, WAFBlocked those the Core Rule Set refused, and
-	// TokenRefused those refused for a missing or wrong token.
-	Limit        int64 `json:"limit"`
-	Attack       int64 `json:"attack"`
-	RuleBlocked  int64 `json:"rule_blocked"`
-	WAFBlocked   int64 `json:"waf_blocked"`
-	TokenRefused int64 `json:"token_refused"`
+	// rule refused, and WAFBlocked those the Core Rule Set refused.
+	Limit       int64 `json:"limit"`
+	Attack      int64 `json:"attack"`
+	RuleBlocked int64 `json:"rule_blocked"`
+	WAFBlocked  int64 `json:"waf_blocked"`
+	// TokenRefused is what a clients.json written by an earlier version gives,
+	// which must still load. Nothing adds to it.
+	TokenRefused int64 `json:"token_refused,omitempty"`
 }
 
 // Request is what a client's history keeps of one of its requests.
 type Request struct {
-	// Forwarded is true for a request passed to the app, Refused for one
-	// refused before anything reached it, a 401 at smallwebwaf's own
-	// endpoints included. Both are false for any other request smallwebwaf
-	// answered there.
+	// Forwarded is true for a request servewaf allowed, and Refused for one it
+	// refused. Both are false for a request for a path under /_smallwebwaf/.
 	Forwarded bool
 	Refused   bool
 	// Status is what the client was sent, 0 if nothing was.
@@ -149,14 +147,12 @@ type Request struct {
 	ResponseBytes int64
 	// BrokeLimit is true for a request that broke a rate limit, a byte
 	// limit or the error burst, Attack for one that matched a ban rule or
-	// asked for a trap path, RuleBlocked for one a block rule refused,
-	// WAFBlocked for one the Core Rule Set refused, and TokenRefused for
-	// one refused for a missing or wrong token.
-	BrokeLimit   bool
-	Attack       bool
-	RuleBlocked  bool
-	WAFBlocked   bool
-	TokenRefused bool
+	// asked for a trap path, RuleBlocked for one a block rule refused, and
+	// WAFBlocked for one the Core Rule Set refused.
+	BrokeLimit  bool
+	Attack      bool
+	RuleBlocked bool
+	WAFBlocked  bool
 }
 
 // New returns a Limiter for limits, with no client counted yet, whose
@@ -334,10 +330,6 @@ func (l *Limiter) AddToHistory(client netip.Prefix, now time.Time, r Request) {
 	if r.WAFBlocked {
 		h.Offences.WAFBlocked++
 	}
-
-	if r.TokenRefused {
-		h.Offences.TokenRefused++
-	}
 }
 
 // AddLookup gives client's history its AS number, AS name and country, as