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: 20000, passed by a client that keeps up 6 a second;
- per day: 300000, passed by a scraper 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

internal/config/config.go

@@ -506,9 +506,9 @@ func FromEnvironment(lookupEnv func(string) (string, bool)) (*Config, error) {
 		AllowNets:               env.netblocks("SWWAF_ALLOW_NETS", ""),
 		RateLimitExemptNets:     env.netblocks("SWWAF_RATE_LIMIT_EXEMPT_NETS", ""),
 		DenyNets:                env.netblocks("SWWAF_DENY_NETS", ""),
-		RateLimitPerMinute:      env.count("SWWAF_RATE_LIMIT_PER_MINUTE", "6000"),
-		RateLimitPerHour:        env.count("SWWAF_RATE_LIMIT_PER_HOUR", "100000"),
-		RateLimitPerDay:         env.count("SWWAF_RATE_LIMIT_PER_DAY", "1000000"),
+		RateLimitPerMinute:      env.count("SWWAF_RATE_LIMIT_PER_MINUTE", "500"),
+		RateLimitPerHour:        env.count("SWWAF_RATE_LIMIT_PER_HOUR", "20000"),
+		RateLimitPerDay:         env.count("SWWAF_RATE_LIMIT_PER_DAY", "300000"),
 		RateLimitExemptPaths:    env.pathPrefixes("SWWAF_RATE_LIMIT_EXEMPT_PATHS", ""),
 		BytesLimitPerMinute:     env.size("SWWAF_BYTES_LIMIT_PER_MINUTE", "4G"),
 		BytesLimitPerHour:       env.size("SWWAF_BYTES_LIMIT_PER_HOUR", "20G"),