feat(#175): Implement E2E test harness

- Create comprehensive E2E test suite for job orchestration
- Add test fixtures for Discord, BullMQ, and Prisma mocks
- Implement 9 end-to-end test scenarios covering:
  * Happy path: webhook → job → step execution → completion
  * Event emission throughout job lifecycle
  * Step failure and retry handling
  * Job failure after max retries
  * Discord command parsing and job creation
  * WebSocket status updates integration
  * Job cancellation workflow
  * Job retry mechanism
  * Progress percentage tracking

- Add helper methods to services for simplified testing:
  * JobStepsService: start(), complete(), fail(), findByJob()
  * RunnerJobsService: updateStatus(), updateProgress()
  * JobEventsService: findByJob()

- Configure vitest.e2e.config.ts for E2E test execution
- All 9 E2E tests passing
- All 1405 unit tests passing
- Quality gates: typecheck, lint, build all passing

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/test/fixtures/mock-discord.fixture.ts

@@ -0,0 +1,72 @@
+import { vi } from "vitest";
+import type { Client, Message, TextChannel } from "discord.js";
+
+/**
+ * Mock Discord client for testing
+ */
+export function createMockDiscordClient(): Partial<Client> {
+  const mockChannel: Partial<TextChannel> = {
+    send: vi.fn().mockResolvedValue({
+      id: "mock-message-id",
+      content: "Mock message sent",
+    }),
+    id: "mock-channel-id",
+    name: "test-channel",
+  };
+
+  return {
+    channels: {
+      fetch: vi.fn().mockResolvedValue(mockChannel),
+      cache: {
+        get: vi.fn().mockReturnValue(mockChannel),
+      },
+    } as never,
+    on: vi.fn(),
+    once: vi.fn(),
+    login: vi.fn().mockResolvedValue("mock-token"),
+    destroy: vi.fn().mockResolvedValue(undefined),
+  };
+}
+
+/**
+ * Mock Discord message for testing command parsing
+ */
+export function createMockDiscordMessage(
+  content: string,
+  overrides?: Partial<Message>
+): Partial<Message> {
+  return {
+    content,
+    author: {
+      id: "mock-user-id",
+      username: "test-user",
+      bot: false,
+      discriminator: "0001",
+      avatar: null,
+      tag: "test-user#0001",
+    } as never,
+    channel: {
+      id: "mock-channel-id",
+      type: 0, // GuildText
+      send: vi.fn().mockResolvedValue({
+        id: "response-message-id",
+        content: "Response sent",
+      }),
+    } as never,
+    guild: {
+      id: "mock-guild-id",
+      name: "Test Guild",
+    } as never,
+    createdTimestamp: Date.now(),
+    id: "mock-message-id",
+    mentions: {
+      has: vi.fn().mockReturnValue(false),
+      users: new Map(),
+    } as never,
+    reply: vi.fn().mockResolvedValue({
+      id: "reply-message-id",
+      content: "Reply sent",
+    }),
+    ...overrides,
+  };
+}