feat(19.3-01): add cooler.Cache with otter memory and Redis drivers

- Cache: Get, Set, Has, Forget, Remember (degrades on cache errors), Increment, Flush
  with per-entry TTLs under <prefix>cache:
- memory driver on otter v2.3.0 bounded by cache.memory.max_entries; Redis driver
  with SET PX, INCRBY and a Flush limited to SCAN MATCH <prefix>cache:* plus UNLINK
- Install publishes the Cache (sharing one Redis client with the rate limiter);
  FromApp serves jobs and commands without a dial
- new docs/services/caching.md, configuration rows, cooler README

go.mod

@@ -19,6 +19,7 @@ require (
 	github.com/knadh/koanf/providers/env/v2 v2.0.1
 	github.com/knadh/koanf/providers/file v1.2.1
 	github.com/knadh/koanf/v2 v2.3.6
+	github.com/maypok86/otter/v2 v2.3.0
 	github.com/microcosm-cc/bluemonday v1.0.27
 	github.com/nicksnyder/go-i18n/v2 v2.6.1
 	github.com/redis/go-redis/v9 v9.23.0