fix(gateway): close billing, limit, routing and translation gaps

Billing:
- Passthrough SSE streams now bill the usage the upstream reports.
  The gateway falls back to a request-size estimate only on a 2xx
  stream or a truncated JSON body.
- A unified stream that fails after it starts is estimated, not
  billed at zero.
- Billing uses the built-in LiteLLM price table and honours
  modelMeta free: true.
- Pricing entries are validated. Cost arithmetic rounds the total and
  saturates on overflow.
- Gemini thinking tokens count as completion tokens.

Limits and storage:
- A rejected request rolls back its counts on the other scopes, so one
  user cannot lock out a group.
- Redis EXPIRE replies are checked. Keys recreated without a TTL are
  repaired at once.
- A mutating pipeline is not retried after reply bytes arrive.
- History, model totals and target usage report a store outage.

Routing and translation:
- Discovered ids with a provider-like prefix are listed only in
  owner/id form, so listing and routing agree.
- Anthropic and Gemini discovery follows pagination.
- The developer role maps to system.
- stream_options.include_usage is honoured on translated streams.
- tool_choice none keeps tools when history holds tool blocks.
- refusal maps to content_filter. Data URI parameters are stripped.

Streaming, retry and failover:
- SSE accepts CR, LF and CRLF line ends. This closes a CR injection
  path.
- Retry-After is never jittered. A cancelled wait returns the
  context error.
- The watchdog timer stops at end of body.
- Oversized bodies return 413.
- A failed stream ends with an error event.
- Failover restores pre-existing headers. Client cancels do not count
  as provider successes.

Also: "admin" is a reserved provider name. metrics.path must start
with "/". Pricing warnings go to the right gateway instance. The admin
targets view sends access as null or [] so the two states differ.
Upstream organisation headers are stripped. The users-file reload
error is logged once per error. Dead code is removed, and test-only
helpers move to test files.

Claude-Session: https://claude.ai/code/session_01V5jYJNxpDFdJkyyExpADrv

logger.go

@@ -31,6 +31,24 @@ func (g *Gateway) errorf(format string, args ...any) {
 	fmt.Fprintf(os.Stderr, "llmgw[%s] ERROR %s\n", g.name, fmt.Sprintf(format, args...))
 }
 
+// pricingWarn is g's own per-instance pricing-warning sink, passed to
+// costMicrosKnownFor (pricing.go) so an unpriced-model warning always logs
+// under this instance's `llmgw[name]` prefix (finding F11 / review-auth
+// F8, 2026-09 review: a package-level warn func replaced on every New()
+// call made the most recently constructed instance log every other
+// instance's warnings).
+//
+// A plain method, not a stored closure field: it reads g.name fresh on
+// every call, exactly like logf/warnf/errorf above, so there is nothing
+// new to keep in sync across a config reload that rebuilds g.
+func (g *Gateway) pricingWarn(msg string) {
+	if msg == warnCapMessage {
+		g.logf("%s", msg)
+		return
+	}
+	g.logf("pricing: no price configured for model %q; cost will be recorded as 0", msg)
+}
+
 // logAuthEvent logs one authentication attempt, at the point one of
 // authStore.identify's six call sites resolves it. A success logs the
 // resolved user's name alongside the request's method and path. Neither