feat: remove speed limit tunnel binding and add migration cleanup

- Remove tunnel binding UI from speed limit page (no more Select component)
- Remove /api/v1/speed-limit/tunnels route alias
- Simplify CreateSpeedLimit/UpdateSpeedLimit to not accept tunnel parameters
- Add schema migration v4 to clear historical tunnel_id/tunnel_name bindings
- Update contract tests to verify tunnel binding is ignored
- Add limiter sync failure tests for forward-level rate limiting

go-backend/internal/store/repo/repository_migrate_test.go

@@ -1,6 +1,7 @@
 package repo
 
 import (
+	"database/sql"
 	"errors"
 	"testing"
 
@@ -175,3 +176,77 @@ func TestMigrateSchemaReturnsViteConfigMigrationError(t *testing.T) {
 		t.Fatalf("expected error %v, got %v", wantErr, err)
 	}
 }
+
+func TestMigrateSchemaClearsSpeedLimitTunnelBinding(t *testing.T) {
+	db, err := gorm.Open(gsqlite.Open(":memory:"), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	t.Cleanup(func() {
+		sqlDB, _ := db.DB()
+		if sqlDB != nil {
+			_ = sqlDB.Close()
+		}
+	})
+
+	if err := db.Exec(`CREATE TABLE schema_version (version INTEGER NOT NULL DEFAULT 0)`).Error; err != nil {
+		t.Fatalf("create schema_version: %v", err)
+	}
+	if err := db.Exec(`INSERT INTO schema_version(version) VALUES(?)`, 3).Error; err != nil {
+		t.Fatalf("seed schema_version: %v", err)
+	}
+	if err := db.Exec(`
+		CREATE TABLE speed_limit (
+			id INTEGER PRIMARY KEY AUTOINCREMENT,
+			name VARCHAR(100) NOT NULL,
+			speed INTEGER NOT NULL,
+			tunnel_id INTEGER,
+			tunnel_name VARCHAR(100),
+			created_time INTEGER NOT NULL,
+			updated_time INTEGER,
+			status INTEGER NOT NULL
+		)
+	`).Error; err != nil {
+		t.Fatalf("create speed_limit: %v", err)
+	}
+	if err := db.Exec(`
+		INSERT INTO speed_limit(name, speed, tunnel_id, tunnel_name, created_time, updated_time, status)
+		VALUES(?, ?, ?, ?, ?, ?, ?)
+	`, "legacy-speed-limit", 100, 101, "legacy-tunnel", 1, 1, 1).Error; err != nil {
+		t.Fatalf("seed speed_limit: %v", err)
+	}
+
+	originalIDRepair := ensurePostgresIDDefaultsFn
+	ensurePostgresIDDefaultsFn = func(db *gorm.DB) error {
+		return nil
+	}
+	t.Cleanup(func() {
+		ensurePostgresIDDefaultsFn = originalIDRepair
+	})
+
+	if err := migrateSchema(db); err != nil {
+		t.Fatalf("migrateSchema: %v", err)
+	}
+
+	var tunnelID sql.NullInt64
+	var tunnelName sql.NullString
+	if err := db.Raw(`SELECT tunnel_id, tunnel_name FROM speed_limit WHERE name = ?`, "legacy-speed-limit").Row().Scan(&tunnelID, &tunnelName); err != nil {
+		t.Fatalf("query speed_limit: %v", err)
+	}
+	if tunnelID.Valid {
+		t.Fatalf("expected tunnel_id cleared to NULL, got %d", tunnelID.Int64)
+	}
+	if tunnelName.Valid {
+		t.Fatalf("expected tunnel_name cleared to NULL, got %q", tunnelName.String)
+	}
+
+	var schemaVersion int
+	if err := db.Raw(`SELECT version FROM schema_version LIMIT 1`).Row().Scan(&schemaVersion); err != nil {
+		t.Fatalf("query schema_version: %v", err)
+	}
+	if schemaVersion != currentSchemaVersion {
+		t.Fatalf("expected schema version %d, got %d", currentSchemaVersion, schemaVersion)
+	}
+}