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/waf/proxy.go

@@ -86,8 +86,8 @@ type Params struct {
 // Server is the server waf runs, with the parts whose state the state
 // files keep, the lookup database, nil unless SWW_LOOKUP_SOURCE is file, the
 // lists fetched from URLs, which its Run fetches, the DNSBL zones' verdicts,
-// AbuseIPDB's scores and checks spent, and the metrics. RouteWatch, nil while
-// SWW_ROUTEWATCH_URL is unset, keeps its answers in memory only.
+// AbuseIPDB's scores and checks spent, routewatch's answers, and the metrics.
+// RouteWatch is nil while SWW_ROUTEWATCH_URL is unset.
 type Server struct {
 	*http.Server