implement Plunk email driver with comprehensive tests

- Add plunkEmail driver following IEmailDriver interface
- Support single and multiple recipients (up to 5 max per Plunk API)
- Handle both string and { text, html } body formats
- Include sender customization (from, name, reply)
- Add recipient validation and error handling
- Create comprehensive unit tests with 6 test cases
- Export plunkEmail from core drivers index
- Update task list with implementation progress

app/src/core/drivers/email/plunk.spec.ts

@@ -0,0 +1,92 @@
+import { describe, it, expect } from "bun:test";
+import { plunkEmail } from "./plunk";
+
+const ALL_TESTS = !!process.env.ALL_TESTS;
+
+describe.skipIf(ALL_TESTS)("plunk", () => {
+	it.only("should throw on failed", async () => {
+		const driver = plunkEmail({ apiKey: "invalid" });
+		expect(driver.send("foo@bar.com", "Test", "Test")).rejects.toThrow();
+	});
+
+	it("should send an email", async () => {
+		const driver = plunkEmail({
+			apiKey: process.env.PLUNK_API_KEY!,
+			from: "test@example.com",
+		});
+		const response = await driver.send(
+			"test@example.com",
+			"Test Email",
+			"This is a test email",
+		);
+		expect(response).toBeDefined();
+		expect(response.success).toBe(true);
+		expect(response.emails).toBeDefined();
+		expect(response.timestamp).toBeDefined();
+	});
+
+	it("should send HTML email", async () => {
+		const driver = plunkEmail({
+			apiKey: process.env.PLUNK_API_KEY!,
+			from: "test@example.com",
+		});
+		const htmlBody = "<h1>Test Email</h1><p>This is a test email</p>";
+		const response = await driver.send(
+			"test@example.com",
+			"HTML Test",
+			htmlBody,
+		);
+		expect(response).toBeDefined();
+		expect(response.success).toBe(true);
+	});
+
+	it("should send with text and html", async () => {
+		const driver = plunkEmail({
+			apiKey: process.env.PLUNK_API_KEY!,
+			from: "test@example.com",
+		});
+		const response = await driver.send("test@example.com", "Test Email", {
+			text: "This is plain text",
+			html: "<p>This is HTML</p>",
+		});
+		expect(response).toBeDefined();
+		expect(response.success).toBe(true);
+	});
+
+	it("should send to multiple recipients", async () => {
+		const driver = plunkEmail({
+			apiKey: process.env.PLUNK_API_KEY!,
+			from: "test@example.com",
+		});
+		const response = await driver.send(
+			"test@example.com",
+			"Multi-recipient Test",
+			"Test email to multiple recipients",
+			{
+				to: ["test1@example.com", "test2@example.com"],
+			},
+		);
+		expect(response).toBeDefined();
+		expect(response.success).toBe(true);
+		expect(response.emails).toHaveLength(2);
+	});
+
+	it("should throw error for more than 5 recipients", async () => {
+		const driver = plunkEmail({
+			apiKey: process.env.PLUNK_API_KEY!,
+			from: "test@example.com",
+		});
+		expect(
+			driver.send("test@example.com", "Test", "Test", {
+				to: [
+					"test1@example.com",
+					"test2@example.com",
+					"test3@example.com",
+					"test4@example.com",
+					"test5@example.com",
+					"test6@example.com",
+				],
+			}),
+		).rejects.toThrow("Plunk supports a maximum of 5 recipients per email");
+	});
+});