SPEC: each requirement once, lists moved to docs/, repeats and sections dropped

Every requirement the second review found in two to five places is now
stated once, with links from the other places. "Risks the design has to
handle", "Rollout per service" and most of "Architecture" are gone, their
two points of their own moved to "Attack detection" and "Anomaly
thresholds". The request log's fields, the metrics and the image's
contents move to docs/request-log.md, docs/metrics.md and docs/image.md,
each linked from the spec. The off rule names SWWAF_LOOKUP_SOURCE and
SWWAF_WAF_MODE, the reputation bound is given, and the six Core Rule Set
changes are a numbered list.

Model: fable-5-1

docs/request-log.md

@@ -0,0 +1,128 @@
+# The request log's fields
+
+`smallwebwaf` writes one JSON object per line on stdout for every request. The
+requirements are under "Request log" in [`SPEC.md`](../SPEC.md); this file lists
+the fields. A field that does not apply to a request is left out.
+
+## Example
+
+```
+{"type":"request","time":"2026-10-03T12:00:00.123Z","instance":"fsn1app1/gitea","client_ip":"203.0.113.9","method":"GET","scheme":"https","host":"app.example","path":"/","query":"","protocol":"HTTP/1.1","status":200,"request_bytes":0,"response_bytes":5120,"referer":"","user_agent":"curl/8.9.1","request_id":"7Q2NHZ4KJ3VXW5YB6R3MEFTD2A","peer_ip":"172.18.0.2","forwarded_for":"203.0.113.9","client_group":"203.0.113.9/32","asn":"AS64496","as_name":"Example Net","country":"DE","request_headers":{"accept":"*/*"},"response_content_type":"text/html; charset=utf-8","upstream_status":200,"action":"forward","counts":{"minute":1,"hour":12,"day":40,"minute_bytes":5120,"hour_bytes":61440,"day_bytes":204800},"duration_total":3.217,"duration_checks":0.041,"duration_upstream_connect":0.052,"duration_upstream_first_byte":2.874,"duration_upstream_total":3.104}
+```
+
+## Standard web log fields
+
+- `time`: when the request arrived, RFC 3339 with milliseconds, in UTC;
+- `instance`: `SWWAF_INSTANCE_NAME`;
+- `client_ip`, `method`, `scheme`, `host`, `path`, `query`, `protocol`;
+- `status`: what the client was sent, `0` if nothing;
+- `request_bytes` and `response_bytes`: body bytes each way;
+- `referer` and `user_agent`.
+
+## Request detail
+
+- `request_id`: the `X-Request-ID` a trusted proxy sent, or a new random one of
+  26 letters and digits. It goes to the app in `X-Request-ID`.
+- `peer_ip`: the TCP peer, normally traefik.
+- `forwarded_for`: the `X-Forwarded-For` header as received.
+- `client_group`: the client as rate limiting counts it, an IPv4 address as a
+  /32 or an IPv6 group.
+- `asn`, `as_name` and `country`: the client's, as looked up. Each is empty
+  when:
+    - lookups are off;
+    - the client is not looked up;
+    - the source cannot place the client;
+    - GeoJS had not answered by the time the request went on.
+- `content_type` and `content_length`: the request's own.
+- `request_headers`: the headers listed in `SWWAF_LOG_REQUEST_HEADERS`, by name
+  in lower case.
+- `has_authorization` and `has_cookie`: true when the request had those headers.
+  Their values are never logged.
+- `websocket`: true when the app switched the connection to another protocol.
+
+## Response detail
+
+- `upstream_status`: what the app answered. It differs from `status` when
+  `smallwebwaf` answered itself.
+- `response_content_type`, `cache_control` and `location`: the answer's headers.
+- `aborted`: true when the client went away early.
+
+## Decision
+
+- `action`: what was done:
+    - `forward`: passed to the app;
+    - `denied`: refused for `SWWAF_DENY_NETS`, or for a reputation source with
+      the action `deny`;
+    - `banned`: refused under a ban, or for a `ban` rule, a trap path or a
+      CrowdSec decision, each of which bans the client;
+    - `country_denied`, `rate_limited`, `rule_blocked` and `waf_blocked`:
+      refused by that check;
+    - `too_large` and `timed_out`: a size or time limit was passed;
+    - `upstream_error`: the app could not be reached, or its answer broke off;
+    - `admin`: answered at one of `smallwebwaf`'s own endpoints.
+- `would_action`: in `observe` mode, what `enforce` mode would have done with a
+  request it would have refused. `action` then names what was done, normally
+  `forward`.
+- `limit_percent` and `limit_percent_setting`: the client's percentage of the
+  rate limits and the setting that lowered it, when one did. `bytes_percent` and
+  `bytes_percent_setting` do the same for the byte limits.
+- `counts`: the client's requests in the minute, hour and day as rate limiting
+  counts them, this request included, as `minute`, `hour` and `day`; its bytes
+  as `minute_bytes`, `hour_bytes` and `day_bytes`. A count can have a fraction,
+  since each window is counted in two buckets with the earlier one weighted.
+  `counts` is left out when rate limiting did not count the request.
+- `limit_hit`: the limit broken: `minute`, `hour` or `day` for a rate limit;
+  `minute_bytes`, `hour_bytes` or `day_bytes` for a byte limit; or
+  `error_burst`. A request whose bytes broke a limit was passed on whole, so its
+  `action` stays `forward`.
+- `rule_ids`: the rule file rules that matched, in order, up to the one that
+  refused.
+- `waf_score` and `waf_rule_ids`: the Core Rule Set's score and the rules that
+  matched, for a request it inspected.
+- `reputation`: the sources the client is on, in this order:
+    - blocklist URLs;
+    - the CrowdSec decision list's URL;
+    - DNS blocklist zones;
+    - `abuseipdb`.
+- `offence`: the kind of offence recorded, when one was.
+- `ban_expires`: when the client's ban ends, for a request that made one or was
+  refused under one: a time, or `permanent`.
+
+## Timings
+
+All in milliseconds:
+
+- `duration_total`: from the request's headers being read to its log line;
+- `duration_checks`: to the end of the checks, before forwarding;
+- `duration_waf`: the part of that the Core Rule Set took;
+- `duration_upstream_connect`: from the hand-over to the app until there was a
+  connection;
+- `duration_upstream_first_byte`: until the first byte of the answer;
+- `duration_upstream_total`: until the end of the answer.
+
+## Every line
+
+Every line has `type`, the standard web log fields, `request_id`, `peer_ip`,
+`client_group`, `asn`, `as_name`, `country`, `action` and `duration_total`. The
+process's own messages share the stream with `"type":"process"`; request lines
+carry `"type":"request"`.
+
+## Sending the log to a syslog server
+
+While `SWWAF_LOG_REMOTE_URL` is set, every line on stdout is also sent to that
+server, as the message of an RFC 5424 syslog record. Over UDP each record is one
+datagram. Over TCP and TLS each record follows its length in bytes and a space.
+stdout is unchanged. The record carries:
+
+- the facility from `SWWAF_LOG_REMOTE_FACILITY`;
+- the severity informational;
+- the time;
+- the host's name;
+- the app name from `SWWAF_LOG_REMOTE_APP_NAME`.
+
+Lines wait in a buffer of `SWWAF_LOG_REMOTE_BUFFER` lines, so a server that is
+slow or down never holds up a request. When the buffer is full, the oldest line
+is dropped. A failed connection is tried again a second later, and twice as long
+after each further failure, up to a minute. A line too long for one UDP datagram
+is dropped alone. As `smallwebwaf` stops, it spends at most two seconds sending
+the lines still waiting, and drops the rest. stdout has carried them.