Fix email delivery and body battery null handling

- Add PocketBase admin auth to notifications endpoint (was returning 0 users)
- Store null instead of 100 for body battery when Garmin returns no data
- Update decision engine to skip body battery rules when values are null
- Dashboard and email already display "N/A" for null values

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

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

@@ -3,6 +3,7 @@
 import { NextResponse } from "next/server";
 
 import { sendDailyEmail } from "@/lib/email";
+import { logger } from "@/lib/logger";
 import { getNutritionGuidance } from "@/lib/nutrition";
 import { createPocketBaseClient } from "@/lib/pocketbase";
 import type { DailyLog, DecisionStatus, User } from "@/types";
@@ -90,8 +91,35 @@ export async function POST(request: Request) {
 
   const pb = createPocketBaseClient();
 
+  // Authenticate as admin to bypass API rules and list all users
+  const adminEmail = process.env.POCKETBASE_ADMIN_EMAIL;
+  const adminPassword = process.env.POCKETBASE_ADMIN_PASSWORD;
+  if (!adminEmail || !adminPassword) {
+    logger.error("Missing POCKETBASE_ADMIN_EMAIL or POCKETBASE_ADMIN_PASSWORD");
+    return NextResponse.json(
+      { error: "Server misconfiguration" },
+      { status: 500 },
+    );
+  }
+
+  try {
+    await pb
+      .collection("_superusers")
+      .authWithPassword(adminEmail, adminPassword);
+  } catch (authError) {
+    logger.error(
+      { err: authError },
+      "Failed to authenticate as PocketBase admin",
+    );
+    return NextResponse.json(
+      { error: "Database authentication failed" },
+      { status: 500 },
+    );
+  }
+
   // Fetch all users
   const users = await pb.collection("users").getFullList<User>();
+  logger.info({ userCount: users.length }, "Fetched users for notifications");
 
   // Get today's date for querying daily logs
   const today = new Date().toISOString().split("T")[0];