refactor: replace global channel registry with instance-based Registry and interface-driven adapters

- Replace global channelRegistry singleton with explicit *Registry passed via dependency injection
- Split monolithic manager.go into connection.go (lifecycle), inbound.go (dispatch), outbound.go (pipeline)
- Introduce optional adapter interfaces: ConfigNormalizer, TargetResolver, BindingMatcher
- Move Descriptor() to Adapter interface, remove init()-based registration
- Relocate SessionHub to adapters/local package
- Extract shared UUID/time helpers to internal/db/uuid.go
- Decompose ConfigStore into fine-grained interfaces: ConfigLister, ConfigResolver, BindingStore, SessionStore

internal/db/uuid.go

@@ -0,0 +1,42 @@
+package db
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+// ParseUUID converts a string UUID to pgtype.UUID.
+func ParseUUID(id string) (pgtype.UUID, error) {
+	parsed, err := uuid.Parse(strings.TrimSpace(id))
+	if err != nil {
+		return pgtype.UUID{}, fmt.Errorf("invalid UUID: %w", err)
+	}
+	var pgID pgtype.UUID
+	pgID.Valid = true
+	copy(pgID.Bytes[:], parsed[:])
+	return pgID, nil
+}
+
+// UUIDToString converts a pgtype.UUID to its string representation.
+func UUIDToString(value pgtype.UUID) string {
+	if !value.Valid {
+		return ""
+	}
+	parsed, err := uuid.FromBytes(value.Bytes[:])
+	if err != nil {
+		return ""
+	}
+	return parsed.String()
+}
+
+// TimeFromPg converts a pgtype.Timestamptz to time.Time.
+func TimeFromPg(value pgtype.Timestamptz) time.Time {
+	if value.Valid {
+		return value.Time
+	}
+	return time.Time{}
+}