Default request limits per minute, hour and 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 abusive bots:

- per minute: 500, room for a fleet's busiest minute and a few first
  visits with an empty cache, and passed within seconds by a client
  firing as fast as it can;
- per hour: 30000, which a client at the minute limit for a whole
  hour reaches exactly;
- per day: 300000, passed by a crawler 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; docs/gitea.md redoes the Actions
runner sums.

Judgement call: the docs/alerts.md ban example shows the minute limit.

Model: opus-5-5

docs/alerts.md

@@ -35,34 +35,34 @@ on one line:
 ```json
 {
     "instance": "fsn1app1/gitea",
-    "time": "2026-10-06T12:00:00.123461Z",
+    "time": "2026-10-06T12:00:50.123461Z",
     "event": "ban",
     "client": "203.0.113.9",
     "netblock": "203.0.113.9/32",
     "asn": "",
     "as_name": "",
     "country": "",
-    "reason": "requests per minute over the limit of 6000",
+    "reason": "requests per minute over the limit of 500",
     "detail": {
-        "ban_expires": "2026-10-06T13:00:00.123Z",
+        "ban_expires": "2026-10-06T13:00:50.123Z",
         "cause": "limit",
         "notes": {
             "asn": "",
             "as_name": "",
             "country": "",
             "kind": "requests",
-            "limit": 6000,
+            "limit": 500,
             "window": "minute",
-            "count": 6001,
+            "count": 501,
             "request": {
-                "time": "2026-10-06T12:00:00.123456789Z",
+                "time": "2026-10-06T12:00:50.123456789Z",
                 "method": "GET",
                 "host": "app.example",
-                "path": "/owner/repo/commits/branch/main?page=812",
+                "path": "/owner/repo/commits/branch/main?page=501",
                 "status": 403,
                 "user_agent": "scraper/1.0"
             },
-            "requests": 8210,
+            "requests": 501,
             "refused": 0,
             "earlier_bans": {
                 "limit": 0,
@@ -89,7 +89,7 @@ on one line:
 - `asn`, `as_name` and `country`: the client's, as known when the alert was
   raised. They are empty when GeoJS had not answered yet.
 - `reason`: a short sentence, such as
-  `requests per minute over the limit of 6000` or `listed by a blocklist`.
+  `requests per minute over the limit of 500` or `listed by a blocklist`.
 - `detail`: what is particular to the event:
     - for a ban, its `cause`, `ban_expires` and `notes` (the notes are listed
       under `bans.json` in [`state-files.md`](state-files.md));