New defaults for the request and byte limits (closes #161)

The request limits and the hour and day byte limits now sit about twice
above what 40 people busy with heavy web apps make together on one
address:

- requests: 6000 a minute, 100,000 an hour, 1,000,000 a day;
- bytes: 20 GiB an hour, 200 GiB a day.

The largest response drops from 5 GiB to 1 GiB. The minute byte limit
of 4 GiB is sized to hold two of the largest responses with their
requests. SPEC.md gives the new reasoning; README.md and the reference
documents give the new figures.

Model: opus-5-5

docs/alerts.md

@@ -42,7 +42,7 @@ on one line:
     "asn": "",
     "as_name": "",
     "country": "",
-    "reason": "requests per minute over the limit of 1000",
+    "reason": "requests per minute over the limit of 6000",
     "detail": {
         "ban_expires": "2026-10-06T13:00:00.123Z",
         "cause": "limit",
@@ -51,9 +51,9 @@ on one line:
             "as_name": "",
             "country": "",
             "kind": "requests",
-            "limit": 1000,
+            "limit": 6000,
             "window": "minute",
-            "count": 1001,
+            "count": 6001,
             "request": {
                 "time": "2026-10-06T12:00:00.123456789Z",
                 "method": "GET",
@@ -62,7 +62,7 @@ on one line:
                 "status": 403,
                 "user_agent": "scraper/1.0"
             },
-            "requests": 5210,
+            "requests": 8210,
             "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 1000` or `listed by a blocklist`.
+  `requests per minute over the limit of 6000` 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));