Initial project setup for PhaseFlow

Set up Next.js 16 project with TypeScript for a training decision app
that integrates menstrual cycle phases with Garmin biometrics for
Hashimoto's thyroiditis management.

Stack: Next.js 16, React 19, Tailwind/shadcn, PocketBase, Drizzle,
Zod, Resend, Vitest, Biome, Lefthook, Nix dev environment.

Includes:
- 7 page routes (dashboard, login, settings, calendar, history, plan)
- 12 API endpoints (garmin, user, cycle, calendar, overrides, cron)
- Core lib utilities (decision engine, cycle phases, nutrition, ICS)
- Type definitions and component scaffolding
- Python script for Garmin token bootstrapping
- Initial unit tests for cycle utilities

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

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

src/lib/email.ts

@@ -0,0 +1,83 @@
+// ABOUTME: Email sending utilities using Resend.
+// ABOUTME: Sends daily training notifications and period confirmation emails.
+import { Resend } from "resend";
+
+const resend = new Resend(process.env.RESEND_API_KEY);
+
+const EMAIL_FROM = process.env.EMAIL_FROM || "phaseflow@example.com";
+
+export interface DailyEmailData {
+  to: string;
+  cycleDay: number;
+  phase: string;
+  decision: {
+    status: string;
+    reason: string;
+    icon: string;
+  };
+  bodyBatteryCurrent: number | null;
+  bodyBatteryYesterdayLow: number | null;
+  hrvStatus: string;
+  weekIntensity: number;
+  phaseLimit: number;
+  remainingMinutes: number;
+  seeds: string;
+  carbRange: string;
+  ketoGuidance: string;
+}
+
+export async function sendDailyEmail(data: DailyEmailData): Promise<void> {
+  const subject = `Today's Training: ${data.decision.icon} ${data.decision.status}`;
+
+  const body = `Good morning!
+
+📅 CYCLE DAY: ${data.cycleDay} (${data.phase})
+
+💪 TODAY'S PLAN:
+${data.decision.icon} ${data.decision.reason}
+
+📊 YOUR DATA:
+• Body Battery Now: ${data.bodyBatteryCurrent ?? "N/A"}
+• Yesterday's Low: ${data.bodyBatteryYesterdayLow ?? "N/A"}
+• HRV Status: ${data.hrvStatus}
+• Week Intensity: ${data.weekIntensity} / ${data.phaseLimit} minutes
+• Remaining: ${data.remainingMinutes} minutes
+
+🌱 SEEDS: ${data.seeds}
+
+🍽️ MACROS: ${data.carbRange}
+🥑 KETO: ${data.ketoGuidance}
+
+---
+Auto-generated by PhaseFlow`;
+
+  await resend.emails.send({
+    from: EMAIL_FROM,
+    to: data.to,
+    subject,
+    text: body,
+  });
+}
+
+export async function sendPeriodConfirmationEmail(
+  to: string,
+  lastPeriodDate: Date,
+  cycleLength: number,
+): Promise<void> {
+  const subject = "🔵 Period Tracking Updated";
+
+  const body = `Your cycle has been reset. Last period: ${lastPeriodDate.toLocaleDateString()}
+Phase calendar updated for next ${cycleLength} days.
+
+Your calendar will update automatically within 24 hours.
+
+---
+Auto-generated by PhaseFlow`;
+
+  await resend.emails.send({
+    from: EMAIL_FROM,
+    to,
+    subject,
+    text: body,
+  });
+}