feat(scenarios): add step title, scenario credentials, and environment context in executor

- add nullable title column to scenario steps; exposed in create/edit forms and step table
- add scenario-credential join (many-to-many with CredentialEntity) with CRUD endpoints
- expose environment URLs in code executor helpers via helpers.env and helpers.getEnvUrl()
- resolve and cache environment per run from the login step's environmentName in scheduler
- add section spacing and step table title column to ScenarioDetailPage

server/src/credential/credential.entity.ts

@@ -0,0 +1,28 @@
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  CreateDateColumn,
+  UpdateDateColumn,
+} from "typeorm";
+
+@Entity("credentials")
+export class CredentialEntity {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  @Column()
+  name: string;
+
+  @Column("text", { nullable: true })
+  data: string | null;
+
+  @Column({ type: "datetime", nullable: true })
+  lastUsedAt: Date | null;
+
+  @CreateDateColumn()
+  createdAt: Date;
+
+  @UpdateDateColumn()
+  updatedAt: Date;
+}