Fix critical bug: cycle phase boundaries now scale with cycle length

CRITICAL BUG FIX:
- Phase boundaries were hardcoded for 31-day cycle, breaking correct
  phase calculations for users with different cycle lengths (28, 35, etc.)
- Added getPhaseBoundaries(cycleLength) function in cycle.ts
- Updated getPhase() to accept cycleLength parameter (default 31)
- Updated all callers (API routes, components) to pass cycleLength
- Added 13 new tests for phase boundaries with 28, 31, and 35-day cycles

ICS IMPROVEMENTS:
- Fixed emojis to match calendar.md spec: 🩸🌱🌸🌙🌑
- Added CATEGORIES field for calendar app colors per spec:
  MENSTRUAL=Red, FOLLICULAR=Green, OVULATION=Pink,
  EARLY_LUTEAL=Yellow, LATE_LUTEAL=Orange
- Added 5 new tests for CATEGORIES

Updated IMPLEMENTATION_PLAN.md with discovered issues and test counts.

825 tests passing (up from 807)

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

src/app/api/cycle/current/route.ts

@@ -3,36 +3,41 @@
 import { NextResponse } from "next/server";
 
 import { withAuth } from "@/lib/auth-middleware";
-import {
-  getCycleDay,
-  getPhase,
-  getPhaseConfig,
-  PHASE_CONFIGS,
-} from "@/lib/cycle";
+import { getCycleDay, getPhase, getPhaseConfig } from "@/lib/cycle";
+
+// Phase boundaries per spec: MENSTRUAL 1-3, FOLLICULAR 4-(cl-16), OVULATION (cl-15)-(cl-14),
+// EARLY_LUTEAL (cl-13)-(cl-7), LATE_LUTEAL (cl-6)-cl
+function getNextPhaseStart(currentPhase: string, cycleLength: number): number {
+  switch (currentPhase) {
+    case "MENSTRUAL":
+      return 4; // FOLLICULAR starts at 4
+    case "FOLLICULAR":
+      return cycleLength - 15; // OVULATION starts at (cycleLength - 15)
+    case "OVULATION":
+      return cycleLength - 13; // EARLY_LUTEAL starts at (cycleLength - 13)
+    case "EARLY_LUTEAL":
+      return cycleLength - 6; // LATE_LUTEAL starts at (cycleLength - 6)
+    case "LATE_LUTEAL":
+      return 1; // New cycle starts
+    default:
+      return 1;
+  }
+}
 
 /**
  * Calculates the number of days until the next phase begins.
  * For LATE_LUTEAL, calculates days until new cycle starts (MENSTRUAL).
  */
 function getDaysUntilNextPhase(cycleDay: number, cycleLength: number): number {
-  const currentPhase = getPhase(cycleDay);
-  const currentConfig = getPhaseConfig(currentPhase);
+  const currentPhase = getPhase(cycleDay, cycleLength);
 
   // For LATE_LUTEAL, calculate days until new cycle
   if (currentPhase === "LATE_LUTEAL") {
     return cycleLength - cycleDay + 1;
   }
 
-  // Find next phase start day
-  const currentIndex = PHASE_CONFIGS.findIndex((c) => c.name === currentPhase);
-  const nextConfig = PHASE_CONFIGS[currentIndex + 1];
-
-  if (nextConfig) {
-    return nextConfig.days[0] - cycleDay;
-  }
-
-  // Fallback: days until end of current phase + 1
-  return currentConfig.days[1] - cycleDay + 1;
+  const nextPhaseStart = getNextPhaseStart(currentPhase, cycleLength);
+  return nextPhaseStart - cycleDay;
 }
 
 export const GET = withAuth(async (_request, user) => {
@@ -53,7 +58,7 @@ export const GET = withAuth(async (_request, user) => {
     user.cycleLength,
     new Date(),
   );
-  const phase = getPhase(cycleDay);
+  const phase = getPhase(cycleDay, user.cycleLength);
   const phaseConfig = getPhaseConfig(phase);
   const daysUntilNextPhase = getDaysUntilNextPhase(cycleDay, user.cycleLength);