Caches of outside APIs live in /var/cache/sww (closes #314)

Every cache of answers from an outside service has its own file in `SWW_CACHE_DIR` (default `/var/cache/sww`): `lookups.json` (GeoJS), `lists.json` (lists fetched by URL, CrowdSec's decisions included), `dnsbl.json`, `abuseipdb-scores.json` and `routewatch.json` (at most 100,000 answers, each kept an hour). `reputation.json` is gone; the AbuseIPDB checks spent today stay in `SWW_STATE_DIR` as `abuseipdb-checks-spent.json`, since losing them would spend the daily budget twice.

A cache file never stops the start: one that does not parse is set aside as `<name>.bad` with a `file_error` alert. An unwritable `SWW_CACHE_DIR` stops the start. The `run` script creates the cache directory and gives it to `sww`. The cache directory needs no volume and can be left out of backups.

Model: opus-5-5

internal/reputation/dnsbl_test.go

@@ -389,7 +389,7 @@ func TestVerdictsKeptAcrossARestart(t *testing.T) {
 			t.Errorf("verdicts %+v, want %+v", kept, want)
 		}
 
-		// Restarted an hour later with what reputation.json keeps, it uses
+		// Restarted an hour later with what dnsbl.json keeps, it uses
 		// the verdicts, and asks the zone nothing, until the TTL has passed
 		// since they were fetched.
 		time.Sleep(time.Hour)
@@ -446,7 +446,7 @@ func TestAtMost100000VerdictsKeptTheOneFetchedLongestAgoDroppedFirst(t *testing.
 	p.Now = func() time.Time { return now }
 	dnsbl := reputation.NewDNSBL(p)
 
-	// 100,001 verdicts, listed by client, as reputation.json lists them,
+	// 100,001 verdicts, listed by client, as dnsbl.json lists them,
 	// each fetched a millisecond before the one before it: the last is one
 	// too many.
 	const count = 100001