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/ics.ts

@@ -0,0 +1,97 @@
+// ABOUTME: ICS calendar feed generation for cycle phase events.
+// ABOUTME: Creates subscribable calendar with phase blocks and warnings.
+import { createEvents, type EventAttributes } from "ics";
+
+import { getCycleDay, getPhase, PHASE_CONFIGS } from "./cycle";
+
+const PHASE_EMOJIS: Record<string, string> = {
+  MENSTRUAL: "🔵",
+  FOLLICULAR: "🟢",
+  OVULATION: "🟣",
+  EARLY_LUTEAL: "🟡",
+  LATE_LUTEAL: "🔴",
+};
+
+interface IcsGeneratorOptions {
+  lastPeriodDate: Date;
+  cycleLength: number;
+  monthsAhead?: number;
+}
+
+export function generateIcsFeed(options: IcsGeneratorOptions): string {
+  const { lastPeriodDate, cycleLength, monthsAhead = 3 } = options;
+  const events: EventAttributes[] = [];
+
+  const endDate = new Date();
+  endDate.setMonth(endDate.getMonth() + monthsAhead);
+
+  const currentDate = new Date(lastPeriodDate);
+  let currentPhase = getPhase(
+    getCycleDay(lastPeriodDate, cycleLength, currentDate),
+  );
+  let phaseStartDate = new Date(currentDate);
+
+  while (currentDate <= endDate) {
+    const cycleDay = getCycleDay(lastPeriodDate, cycleLength, currentDate);
+    const phase = getPhase(cycleDay);
+
+    // Add warning events
+    if (cycleDay === 22) {
+      events.push({
+        start: dateToArray(currentDate),
+        end: dateToArray(currentDate),
+        title: "⚠️ Late Luteal Phase Starts in 3 Days",
+        description: "Begin reducing training intensity",
+      });
+    }
+
+    if (cycleDay === 25) {
+      events.push({
+        start: dateToArray(currentDate),
+        end: dateToArray(currentDate),
+        title: "🔴 CRITICAL PHASE - Gentle Rebounding Only!",
+        description: "Late luteal phase - protect your cycle",
+      });
+    }
+
+    // Track phase changes
+    if (phase !== currentPhase) {
+      // Close previous phase event
+      events.push(createPhaseEvent(currentPhase, phaseStartDate, currentDate));
+      currentPhase = phase;
+      phaseStartDate = new Date(currentDate);
+    }
+
+    currentDate.setDate(currentDate.getDate() + 1);
+  }
+
+  // Close final phase
+  events.push(createPhaseEvent(currentPhase, phaseStartDate, currentDate));
+
+  const { value, error } = createEvents(events);
+  if (error) {
+    throw new Error(`ICS generation error: ${error}`);
+  }
+
+  return value || "";
+}
+
+function createPhaseEvent(
+  phase: string,
+  startDate: Date,
+  endDate: Date,
+): EventAttributes {
+  const config = PHASE_CONFIGS.find((c) => c.name === phase);
+  const emoji = PHASE_EMOJIS[phase] || "📅";
+
+  return {
+    start: dateToArray(startDate),
+    end: dateToArray(endDate),
+    title: `${emoji} ${phase.replace("_", " ")}`,
+    description: config?.trainingType || "",
+  };
+}
+
+function dateToArray(date: Date): [number, number, number, number, number] {
+  return [date.getFullYear(), date.getMonth() + 1, date.getDate(), 0, 0];
+}