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/today/route.ts

@@ -8,7 +8,6 @@ import {
   getPhase,
   getPhaseConfig,
   getPhaseLimit,
-  PHASE_CONFIGS,
 } from "@/lib/cycle";
 import { getDecisionWithOverrides } from "@/lib/decision-engine";
 import { logger } from "@/lib/logger";
@@ -47,21 +46,25 @@ 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 phaseLimit = getPhaseLimit(phase);
 
-  // Calculate days until next phase
-  const currentPhaseIndex = PHASE_CONFIGS.findIndex((c) => c.name === phase);
-  const nextPhaseIndex = (currentPhaseIndex + 1) % PHASE_CONFIGS.length;
-  const nextPhaseStartDay = PHASE_CONFIGS[nextPhaseIndex].days[0];
-
+  // Calculate days until next phase using dynamic boundaries
+  // Phase boundaries: MENSTRUAL 1-3, FOLLICULAR 4-(cl-16), OVULATION (cl-15)-(cl-14),
+  // EARLY_LUTEAL (cl-13)-(cl-7), LATE_LUTEAL (cl-6)-cl
   let daysUntilNextPhase: number;
-  if (nextPhaseIndex === 0) {
-    // Currently in LATE_LUTEAL, next phase is MENSTRUAL (start of new cycle)
+  if (phase === "LATE_LUTEAL") {
     daysUntilNextPhase = user.cycleLength - cycleDay + 1;
+  } else if (phase === "MENSTRUAL") {
+    daysUntilNextPhase = 4 - cycleDay;
+  } else if (phase === "FOLLICULAR") {
+    daysUntilNextPhase = user.cycleLength - 15 - cycleDay;
+  } else if (phase === "OVULATION") {
+    daysUntilNextPhase = user.cycleLength - 13 - cycleDay;
   } else {
-    daysUntilNextPhase = nextPhaseStartDay - cycleDay;
+    // EARLY_LUTEAL
+    daysUntilNextPhase = user.cycleLength - 6 - cycleDay;
   }
 
   // Try to fetch today's DailyLog for biometrics