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/ops/app/kol_subscription_cache_test.go

@@ -18,15 +18,28 @@ func (c *recordingCache) Get(context.Context, string) ([]byte, error) {
 	return nil, sharedcache.ErrNotFound
 }
 
+func (c *recordingCache) GetMulti(context.Context, []string) (map[string][]byte, error) {
+	return map[string][]byte{}, nil
+}
+
 func (c *recordingCache) Set(context.Context, string, []byte, time.Duration) error {
 	return nil
 }
 
+func (c *recordingCache) SetMulti(context.Context, []sharedcache.Item) error {
+	return nil
+}
+
 func (c *recordingCache) Delete(_ context.Context, key string) error {
 	c.deletedKeys = append(c.deletedKeys, key)
 	return nil
 }
 
+func (c *recordingCache) DeleteMany(_ context.Context, keys []string) error {
+	c.deletedKeys = append(c.deletedKeys, keys...)
+	return nil
+}
+
 func (c *recordingCache) DeletePrefix(_ context.Context, prefix string) error {
 	c.deletedPrefixes = append(c.deletedPrefixes, prefix)
 	return nil