Add unit tests for lib utilities (P3.2-P3.6)

Implement comprehensive test coverage for five library modules:

- encryption.test.ts (14 tests): AES-256-GCM encrypt/decrypt round-trip,
  ciphertext format validation, error handling, key padding/truncation
- nutrition.test.ts (17 tests): seed cycling by cycle day, carb ranges
  by phase, keto guidance by phase, seed switch alert on day 15
- garmin.test.ts (14 tests): token expiry checks, days until expiry
  calculation, API fetch with auth headers, error handling
- email.test.ts (14 tests): daily email composition with biometrics,
  nutrition guidance, period confirmation emails, null value handling
- ics.test.ts (23 tests): ICS format validation, phase events with
  emojis, warning events on days 22/25, cycle length handling

Total: 82 new tests bringing project total to 254 passing tests.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/lib/email.test.ts

@@ -0,0 +1,191 @@
+// ABOUTME: Unit tests for email sending utilities.
+// ABOUTME: Tests email composition, subject lines, and Resend integration.
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+const { mockSend } = vi.hoisted(() => ({
+  mockSend: vi.fn().mockResolvedValue({ id: "mock-email-id" }),
+}));
+
+// Mock the resend module before importing email utilities
+vi.mock("resend", () => ({
+  Resend: class MockResend {
+    emails = { send: mockSend };
+  },
+}));
+
+import type { DailyEmailData } from "./email";
+import { sendDailyEmail, sendPeriodConfirmationEmail } from "./email";
+
+describe("sendDailyEmail", () => {
+  afterEach(() => {
+    vi.clearAllMocks();
+  });
+
+  const sampleData: DailyEmailData = {
+    to: "user@example.com",
+    cycleDay: 15,
+    phase: "OVULATION",
+    decision: {
+      status: "TRAIN",
+      reason: "Body battery high, HRV balanced - great day for training!",
+      icon: "💪",
+    },
+    bodyBatteryCurrent: 85,
+    bodyBatteryYesterdayLow: 45,
+    hrvStatus: "Balanced",
+    weekIntensity: 60,
+    phaseLimit: 80,
+    remainingMinutes: 20,
+    seeds: "Sesame (1-2 tbsp) + Sunflower (1-2 tbsp)",
+    carbRange: "100-150g",
+    ketoGuidance: "No - exit keto, need carbs for ovulation",
+  };
+
+  it("sends email with correct subject line", async () => {
+    await sendDailyEmail(sampleData);
+    expect(mockSend).toHaveBeenCalledWith(
+      expect.objectContaining({
+        subject: "Today's Training: 💪 TRAIN",
+      }),
+    );
+  });
+
+  it("includes cycle day and phase in email body", async () => {
+    await sendDailyEmail(sampleData);
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain("📅 CYCLE DAY: 15 (OVULATION)");
+  });
+
+  it("includes decision icon and reason", async () => {
+    await sendDailyEmail(sampleData);
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain(
+      "💪 Body battery high, HRV balanced - great day for training!",
+    );
+  });
+
+  it("includes biometric data in email body", async () => {
+    await sendDailyEmail(sampleData);
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain("Body Battery Now: 85");
+    expect(call.text).toContain("Yesterday's Low: 45");
+    expect(call.text).toContain("HRV Status: Balanced");
+    expect(call.text).toContain("Week Intensity: 60 / 80 minutes");
+    expect(call.text).toContain("Remaining: 20 minutes");
+  });
+
+  it("includes nutrition guidance in email body", async () => {
+    await sendDailyEmail(sampleData);
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain(
+      "🌱 SEEDS: Sesame (1-2 tbsp) + Sunflower (1-2 tbsp)",
+    );
+    expect(call.text).toContain("🍽️ MACROS: 100-150g");
+    expect(call.text).toContain(
+      "🥑 KETO: No - exit keto, need carbs for ovulation",
+    );
+  });
+
+  it("handles null body battery values with N/A", async () => {
+    const dataWithNulls: DailyEmailData = {
+      ...sampleData,
+      bodyBatteryCurrent: null,
+      bodyBatteryYesterdayLow: null,
+    };
+    await sendDailyEmail(dataWithNulls);
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain("Body Battery Now: N/A");
+    expect(call.text).toContain("Yesterday's Low: N/A");
+  });
+
+  it("sends email to correct recipient", async () => {
+    await sendDailyEmail(sampleData);
+    expect(mockSend).toHaveBeenCalledWith(
+      expect.objectContaining({
+        to: "user@example.com",
+      }),
+    );
+  });
+
+  it("includes auto-generated footer", async () => {
+    await sendDailyEmail(sampleData);
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain("Auto-generated by PhaseFlow");
+  });
+});
+
+describe("sendPeriodConfirmationEmail", () => {
+  afterEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("sends email with correct subject", async () => {
+    await sendPeriodConfirmationEmail(
+      "user@example.com",
+      new Date("2025-01-15"),
+      31,
+    );
+    expect(mockSend).toHaveBeenCalledWith(
+      expect.objectContaining({
+        subject: "🔵 Period Tracking Updated",
+      }),
+    );
+  });
+
+  it("includes last period date in body", async () => {
+    await sendPeriodConfirmationEmail(
+      "user@example.com",
+      new Date("2025-01-15"),
+      31,
+    );
+    const call = mockSend.mock.calls[0][0];
+    // Date formatting depends on locale, so check for key parts
+    expect(call.text).toContain("Your cycle has been reset");
+    expect(call.text).toContain("Last period:");
+  });
+
+  it("includes cycle length in body", async () => {
+    await sendPeriodConfirmationEmail(
+      "user@example.com",
+      new Date("2025-01-15"),
+      28,
+    );
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain("Phase calendar updated for next 28 days");
+  });
+
+  it("sends to correct recipient", async () => {
+    await sendPeriodConfirmationEmail(
+      "test@example.com",
+      new Date("2025-01-15"),
+      31,
+    );
+    expect(mockSend).toHaveBeenCalledWith(
+      expect.objectContaining({
+        to: "test@example.com",
+      }),
+    );
+  });
+
+  it("includes auto-generated footer", async () => {
+    await sendPeriodConfirmationEmail(
+      "user@example.com",
+      new Date("2025-01-15"),
+      31,
+    );
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain("Auto-generated by PhaseFlow");
+  });
+
+  it("mentions calendar update timing", async () => {
+    await sendPeriodConfirmationEmail(
+      "user@example.com",
+      new Date("2025-01-15"),
+      31,
+    );
+    const call = mockSend.mock.calls[0][0];
+    expect(call.text).toContain(
+      "Your calendar will update automatically within 24 hours",
+    );
+  });
+});