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/components/dashboard/mini-calendar.tsx

@@ -55,7 +55,7 @@ export function MiniCalendar({
 
   // Calculate current cycle day and phase for the header
   const currentCycleDay = getCycleDay(lastPeriodDate, cycleLength, today);
-  const currentPhase = getPhase(currentCycleDay);
+  const currentPhase = getPhase(currentCycleDay, cycleLength);
 
   const handlePreviousMonth = () => {
     if (displayMonth === 0) {
@@ -154,7 +154,7 @@ export function MiniCalendar({
           }
 
           const cycleDay = getCycleDay(lastPeriodDate, cycleLength, date);
-          const phase = getPhase(cycleDay);
+          const phase = getPhase(cycleDay, cycleLength);
           const isToday =
             date.getFullYear() === today.getFullYear() &&
             date.getMonth() === today.getMonth() &&