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/memory.go

@@ -41,6 +41,25 @@ func (c *memoryCache) Get(_ context.Context, key string) ([]byte, error) {
 	return dst, nil
 }
 
+func (c *memoryCache) GetMulti(ctx context.Context, keys []string) (map[string][]byte, error) {
+	if len(keys) == 0 {
+		return map[string][]byte{}, nil
+	}
+
+	result := make(map[string][]byte, len(keys))
+	for _, key := range keys {
+		value, err := c.Get(ctx, key)
+		if err != nil {
+			if err == ErrNotFound {
+				continue
+			}
+			return nil, err
+		}
+		result[key] = value
+	}
+	return result, nil
+}
+
 func (c *memoryCache) Set(_ context.Context, key string, value []byte, ttl time.Duration) error {
 	dst := make([]byte, len(value))
 	copy(dst, value)
@@ -51,6 +70,15 @@ func (c *memoryCache) Set(_ context.Context, key string, value []byte, ttl time.
 	return nil
 }
 
+func (c *memoryCache) SetMulti(ctx context.Context, items []Item) error {
+	for _, item := range items {
+		if err := c.Set(ctx, item.Key, item.Value, item.TTL); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func (c *memoryCache) Delete(_ context.Context, key string) error {
 	c.mu.Lock()
 	delete(c.entries, key)
@@ -58,6 +86,15 @@ func (c *memoryCache) Delete(_ context.Context, key string) error {
 	return nil
 }
 
+func (c *memoryCache) DeleteMany(ctx context.Context, keys []string) error {
+	for _, key := range keys {
+		if err := c.Delete(ctx, key); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func (c *memoryCache) DeletePrefix(_ context.Context, prefix string) error {
 	if prefix == "" {
 		return nil