feat(cache,worker): overhaul cache layer and add generation task lease recovery

- shared/cache: add Options/L1/async/metrics/prefix decorators, multi-key ops, Redis pool tuning, and JSON readthrough metrics
- worker-generate: claim tasks via DB lease + heartbeat, requeue stale queued tasks, expire dead leases with refund/cache invalidation
- tenant: version article cache keys so worker recovery invalidations propagate cleanly
- shared/config: expand Redis (pool/timeouts/TLS) and Generation (lease/recovery) configs with defaults

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/shared/cache/factory.go

@@ -2,11 +2,39 @@ package cache
 
 import goredis "github.com/redis/go-redis/v9"
 
-func New(driver string, rdb *goredis.Client) Cache {
+func New(driver string, rdb *goredis.Client, opts ...Option) Cache {
+	options := DefaultOptions()
+	for _, opt := range opts {
+		if opt != nil {
+			opt(&options)
+		}
+	}
+	return NewWithOptions(driver, rdb, options)
+}
+
+func NewWithOptions(driver string, rdb *goredis.Client, options Options) Cache {
+	options = normalizeOptions(options)
+
+	var backend Cache
 	switch driver {
 	case "redis":
-		return newRedisCache(rdb)
+		backend = newRedisCache(rdb, options.DeleteScanCount)
 	default:
-		return newMemoryCache()
+		backend = newMemoryCache()
 	}
+
+	if options.Namespace != "" {
+		backend = newPrefixCache(backend, options.Namespace)
+	}
+	if options.L1Enabled && driver == "redis" {
+		backend = newL1Cache(backend, options.L1TTL)
+	}
+	if options.MetricsEnabled {
+		backend = newObservedCache(backend, driver)
+	}
+	if options.AsyncFillEnabled {
+		backend = newAsyncCache(backend, options.AsyncFillWorkers, options.AsyncFillBuffer, options.AsyncFillTimeout)
+	}
+
+	return newOptionsCache(backend, options)
 }