Default request limits per hour and per day, sized for API use (closes #176)

The default request limits now suit programmatic use of an API, such
as an automation fleet on another host, and still catch crawlers:

- per minute: off;
- per hour: 30000, passed by a crawler that keeps up 10 a second;
- per day: 300000, passed by one that keeps up 4 a second.

The byte limits and ban lengths are unchanged. SPEC.md, README.md and
docs/settings.md give the reasons and what counting cannot catch;
docs/gitea.md redoes the Actions runner sums.

Judgement call: the ban alert example in docs/alerts.md now shows the
hour limit, since the minute limit is off by default.

Model: opus-5-5

docs/settings.md

@@ -99,9 +99,18 @@ that take `off`, the `_FILE` form, and what each group does and why.
 
 ## Request rate limits, per client
 
-- `SWWAF_RATE_LIMIT_PER_MINUTE` (default `6000`), `SWWAF_RATE_LIMIT_PER_HOUR`
-  (default `100000`) and `SWWAF_RATE_LIMIT_PER_DAY` (default `1000000`): the
-  most requests a client may make in each window. A count or `off`.
+- `SWWAF_RATE_LIMIT_PER_MINUTE` (default `off`): the most requests a client may
+  make in a minute. A count or `off`. It is off by default so that a short burst
+  of API requests breaks no limit on its own.
+- `SWWAF_RATE_LIMIT_PER_HOUR` (default `30000`, about 8 a second): the most
+  requests a client may make in an hour. A count or `off`. The default leaves
+  room for an automation fleet at work, and catches a crawler that keeps up 10 a
+  second.
+- `SWWAF_RATE_LIMIT_PER_DAY` (default `300000`, about 3.5 a second): the most
+  requests a client may make in a day. A count or `off`. The default catches a
+  crawler that keeps up 4 a second around the clock.
+- Counting cannot catch a client slower than these limits (see "Request rate
+  limits, per client" in [`SPEC.md`](../SPEC.md)).
 - `SWWAF_RATE_LIMIT_EXEMPT_PATHS` (default empty): path prefixes exempt from
   rate limiting and the byte limits, such as `/assets/`.