Fix PocketBase date format - use YYYY-MM-DD instead of ISO

PocketBase filters don't accept ISO format with T separator (causes 400).
Changed both garmin-sync storage and today route query to use simple
YYYY-MM-DD format, matching the working /api/history pattern.

TDD approach: wrote failing tests first, then implemented the fix.

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

src/app/api/today/route.ts

@@ -74,24 +74,16 @@ export const GET = withAuth(async (_request, user, pb) => {
   // Sort by created DESC to get the most recent record if multiple exist
   let biometrics = { ...DEFAULT_BIOMETRICS, phaseLimit };
   try {
-    // Use date range query for proper date field comparison
-    // PocketBase date fields need >= and < operators, not string contains
-    const todayStart = new Date();
-    todayStart.setUTCHours(0, 0, 0, 0);
-    const tomorrowStart = new Date(todayStart.getTime() + 86400000);
-    const todayISO = todayStart.toISOString();
-    const tomorrowISO = tomorrowStart.toISOString();
+    // Use YYYY-MM-DD format with contains operator for PocketBase date field
+    // PocketBase filters don't accept ISO format with T separator
+    const today = new Date().toISOString().split("T")[0];
 
-    logger.info(
-      { userId: user.id, todayISO, tomorrowISO },
-      "Fetching dailyLog",
-    );
+    logger.info({ userId: user.id, date: today }, "Fetching dailyLog");
     const dailyLog = await pb
       .collection("dailyLogs")
-      .getFirstListItem<DailyLog>(
-        `user="${user.id}" && date>="${todayISO}" && date<"${tomorrowISO}"`,
-        { sort: "-created" },
-      );
+      .getFirstListItem<DailyLog>(`user="${user.id}" && date~"${today}"`, {
+        sort: "-created",
+      });
 
     logger.info(
       {