feat: implement moderation message capture system

- Add message store with database operations (insert, update, query)
- Implement attachment uploader with picser integration
- Add Discord event listeners for message create/update/delete
- Support attachment upload with retry logic and error handling
- Add comprehensive unit tests for message store and uploader

tests/moderation/attachmentUploader.test.ts

@@ -0,0 +1,46 @@
+import { describe, it, expect, beforeEach } from "vitest";
+
+beforeEach(() => {
+  process.env = {
+    ...process.env,
+    DISCORD_TOKEN: "test-token",
+    MONITOR_GUILD_ID: "test-guild",
+    NODE_ENV: "test",
+  };
+});
+
+describe("attachmentUploader", () => {
+  it("parses picser upload response correctly", async () => {
+    const { parseUploadResponse } = await import("../../src/moderation/attachmentUploader");
+
+    const response = {
+      success: true,
+      filename: "uploads/abc123.jpg",
+      urls: {
+        raw_commit: "https://raw.githubusercontent.com/user/repo/commit/uploads/abc123.jpg",
+      },
+      size: 102400,
+      type: "image/jpeg",
+    };
+
+    const result = parseUploadResponse(response);
+
+    expect(result.success).toBe(true);
+    expect(result.url).toBe("https://raw.githubusercontent.com/user/repo/commit/uploads/abc123.jpg");
+    expect(result.filename).toBe("uploads/abc123.jpg");
+  });
+
+  it("handles upload response with missing raw_commit", async () => {
+    const { parseUploadResponse } = await import("../../src/moderation/attachmentUploader");
+
+    const response = {
+      success: true,
+      filename: "uploads/abc123.jpg",
+      urls: {},
+      size: 102400,
+      type: "image/jpeg",
+    };
+
+    expect(() => parseUploadResponse(response)).toThrow();
+  });
+});