Say which bytes the byte limits count, and what passing one does (closes #203)

Documents only. The byte limits and byte anomaly thresholds count body
bytes, as SWW_BYTES_COUNT chooses them, with WebSocket traffic each way,
once a response has ended; the request that passes a limit is not cut
off and the client is banned. README.md, SPEC.md and docs/ now say so,
and no longer call a response's bytes the request's. Also made plain:
rate limits and their exemptions, the refusal threshold,
SWRP_MAX_REQUEST_TIME_MS, SWRP_MAX_RESPONSE_SIZE, SWW_LOOKUP_SOURCE,
SWW_LIMIT_BAN_REPEAT_WINDOW, the metrics' byte series, and the SPEC.md
claim about answering within SWRP_TIMEOUT_MS. EVALUATION.md is audited
too; its survey facts and date are unchanged.

Model: fable-5-1 (first audit); opus-5-5 (rework)

docs/metrics.md

@@ -5,6 +5,9 @@ What `GET /_sww/metrics` answers with, at `discriminator`'s own address.
 keeps the `instance` label as `exported_instance` unless the scrape sets
 `honor_labels: true`. `rproxy` has no metrics.
 
+Every `sww_*request_bytes_total` and `sww_*response_bytes_total` series counts
+body bytes, never headers, whatever `SWW_BYTES_COUNT` says.
+
 ## Traffic
 
 - `sww_requests_total`, `sww_request_bytes_total` and