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.go

@@ -40,7 +40,7 @@ var (
 	errNotListing = errors.New("the answer is outside 127.0.0.0/8")
 )
 
-// Verdict is what a zone said about a client, as reputation.json holds
+// Verdict is what a zone said about a client, as dnsbl.json holds
 // it: the zone, the client's address, whether the zone lists it, and when
 // the zone answered.
 type Verdict struct {
@@ -187,7 +187,7 @@ func (d *DNSBL) Failures(zone string) int {
 }
 
 // Snapshot returns every verdict still in use, sorted by client, then by
-// zone, as reputation.json lists them.
+// zone, as dnsbl.json lists them.
 func (d *DNSBL) Snapshot() []Verdict {
 	d.mu.Lock()
 
@@ -209,7 +209,7 @@ func (d *DNSBL) Snapshot() []Verdict {
 	return verdicts
 }
 
-// Load keeps verdicts, read from reputation.json, in place of those it
+// Load keeps verdicts, read from dnsbl.json, in place of those it
 // keeps, but for those of a zone SWW_DNSBL_ZONES does not name, and,
 // past maxVerdicts, those fetched longest ago. One fetched CacheTTL ago or
 // more is neither used nor written, as for any verdict.