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/config/config.go

@@ -191,12 +191,15 @@ type Config struct {
 	BanScopeV4Prefix int
 	// StateDir is the directory of the state files, an absolute path
 	// (SWW_STATE_DIR). bans.json is written StateWriteDelay after a ban
-	// is made (SWW_STATE_WRITE_DELAY), and every state file every
-	// StateCounterInterval (SWW_STATE_COUNTER_INTERVAL). Neither can be
-	// off.
+	// is made (SWW_STATE_WRITE_DELAY), and every state and cache file
+	// every StateCounterInterval (SWW_STATE_COUNTER_INTERVAL). Neither
+	// can be off.
 	StateDir             string
 	StateWriteDelay      time.Duration
 	StateCounterInterval time.Duration
+	// CacheDir is the directory of the cache files, which keep answers
+	// from outside services, an absolute path (SWW_CACHE_DIR).
+	CacheDir string
 	// LogRequestHeaders are the request headers whose values the request
 	// log gives, in lower case (SWW_LOG_REQUEST_HEADERS).
 	LogRequestHeaders []string
@@ -560,6 +563,7 @@ func FromEnvironment(
 		StateDir:             env.absolutePath("SWW_STATE_DIR", "/var/lib/sww"),
 		StateWriteDelay:      env.durationNotOff("SWW_STATE_WRITE_DELAY", "10s"),
 		StateCounterInterval: env.durationNotOff("SWW_STATE_COUNTER_INTERVAL", "15m"),
+		CacheDir:             env.absolutePath("SWW_CACHE_DIR", "/var/cache/sww"),
 		LogRequestHeaders: env.headerNames("SWW_LOG_REQUEST_HEADERS",
 			"accept,accept-language,accept-encoding,content-type,origin,range"),
 		LogLevel:            env.logLevel("SWW_LOG_LEVEL", "info"),