Add email sent/failed structured logging

Implement email logging per observability spec:
- Add structured logging for email sent (info level) and failed (error level)
- Include userId, type, and recipient fields in log events
- Add userId parameter to email functions (sendDailyEmail, sendPeriodConfirmationEmail, sendTokenExpirationWarning)
- Update cron routes (notifications, garmin-sync) to pass userId

6 new tests added to email.test.ts (now 30 tests total)

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

src/app/api/cron/notifications/route.ts

@@ -121,25 +121,28 @@ export async function POST(request: Request) {
       const nutrition = getNutritionGuidance(dailyLog.cycleDay);
 
       // Send email
-      await sendDailyEmail({
-        to: user.email,
-        cycleDay: dailyLog.cycleDay,
-        phase: dailyLog.phase,
-        decision: {
-          status: dailyLog.trainingDecision,
-          reason: dailyLog.decisionReason,
-          icon: getDecisionIcon(dailyLog.trainingDecision as DecisionStatus),
+      await sendDailyEmail(
+        {
+          to: user.email,
+          cycleDay: dailyLog.cycleDay,
+          phase: dailyLog.phase,
+          decision: {
+            status: dailyLog.trainingDecision,
+            reason: dailyLog.decisionReason,
+            icon: getDecisionIcon(dailyLog.trainingDecision as DecisionStatus),
+          },
+          bodyBatteryCurrent: dailyLog.bodyBatteryCurrent,
+          bodyBatteryYesterdayLow: dailyLog.bodyBatteryYesterdayLow,
+          hrvStatus: dailyLog.hrvStatus,
+          weekIntensity: dailyLog.weekIntensityMinutes,
+          phaseLimit: dailyLog.phaseLimit,
+          remainingMinutes: dailyLog.remainingMinutes,
+          seeds: nutrition.seeds,
+          carbRange: nutrition.carbRange,
+          ketoGuidance: nutrition.ketoGuidance,
         },
-        bodyBatteryCurrent: dailyLog.bodyBatteryCurrent,
-        bodyBatteryYesterdayLow: dailyLog.bodyBatteryYesterdayLow,
-        hrvStatus: dailyLog.hrvStatus,
-        weekIntensity: dailyLog.weekIntensityMinutes,
-        phaseLimit: dailyLog.phaseLimit,
-        remainingMinutes: dailyLog.remainingMinutes,
-        seeds: nutrition.seeds,
-        carbRange: nutrition.carbRange,
-        ketoGuidance: nutrition.ketoGuidance,
-      });
+        user.id,
+      );
 
       // Update notificationSentAt timestamp
       await pb.collection("dailyLogs").update(dailyLog.id, {