feat: implement Redis-based message bus and awareness management

- Added RedisMessageBus for message distribution using Redis Pub/Sub.
- Introduced LocalMessageBus as a no-op implementation for single-server mode.
- Created messagebus interface for abstraction of message distribution.
- Implemented awareness management methods: SetAwareness, GetAllAwareness, DeleteAwareness, and ClearAllAwareness.
- Added logger utility for structured logging with zap.
- Refactored SniffYjsClientIDs and MakeYjsDeleteMessage functions for improved readability.

backend/internal/messagebus/interface.go

@@ -0,0 +1,80 @@
+package messagebus
+
+import (
+	"context"
+)
+
+// MessageBus abstracts message distribution across server instances
+type MessageBus interface {
+	// Publish sends a message to a specific room channel
+	// data must be preserved as-is (binary safe)
+	Publish(ctx context.Context, roomID string, data []byte) error
+
+	// Subscribe listens to messages for a specific room
+	// Returns a channel that receives binary messages
+	Subscribe(ctx context.Context, roomID string) (<-chan []byte, error)
+
+	// Unsubscribe stops listening to a room
+	Unsubscribe(ctx context.Context, roomID string) error
+
+	// SetAwareness caches awareness data for a client in a room
+	SetAwareness(ctx context.Context, roomID string, clientID uint64, data []byte) error
+
+	// GetAllAwareness retrieves all cached awareness for a room
+	GetAllAwareness(ctx context.Context, roomID string) (map[uint64][]byte, error)
+
+	// DeleteAwareness removes awareness cache for a client
+	DeleteAwareness(ctx context.Context, roomID string, clientID uint64) error
+
+	ClearAllAwareness(ctx context.Context, roomID string) error
+
+	// IsHealthy returns true if message bus is operational
+	IsHealthy() bool
+
+	// Close gracefully shuts down the message bus
+	Close() error
+}
+
+// LocalMessageBus is a no-op implementation for single-server mode
+type LocalMessageBus struct{}
+
+func NewLocalMessageBus() *LocalMessageBus {
+	return &LocalMessageBus{}
+}
+
+func (l *LocalMessageBus) Publish(ctx context.Context, roomID string, data []byte) error {
+	return nil // No-op for local mode
+}
+
+func (l *LocalMessageBus) Subscribe(ctx context.Context, roomID string) (<-chan []byte, error) {
+	ch := make(chan []byte)
+	close(ch) // Immediately closed channel
+	return ch, nil
+}
+
+func (l *LocalMessageBus) Unsubscribe(ctx context.Context, roomID string) error {
+	return nil
+}
+
+func (l *LocalMessageBus) SetAwareness(ctx context.Context, roomID string, clientID uint64, data []byte) error {
+	return nil
+}
+
+func (l *LocalMessageBus) GetAllAwareness(ctx context.Context, roomID string) (map[uint64][]byte, error) {
+	return nil, nil
+}
+
+func (l *LocalMessageBus) DeleteAwareness(ctx context.Context, roomID string, clientID uint64) error {
+	return nil
+}
+func (l *LocalMessageBus) ClearAllAwareness(ctx context.Context, roomID string) error {
+	return nil
+}
+
+func (l *LocalMessageBus) IsHealthy() bool {
+	return true
+}
+
+func (l *LocalMessageBus) Close() error {
+	return nil
+}