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.test.ts

@@ -12,6 +12,9 @@ let currentMockUser: User | null = null;
 // Module-level variable to control mock daily log in tests
 let currentMockDailyLog: DailyLog | null = null;
 
+// Track the filter string passed to getFirstListItem
+let lastDailyLogFilter: string | null = null;
+
 // Create mock PocketBase client
 const mockPb = {
   collection: vi.fn((collectionName: string) => ({
@@ -30,7 +33,11 @@ const mockPb = {
       }
       throw new Error("Record not found");
     }),
-    getFirstListItem: vi.fn(async () => {
+    getFirstListItem: vi.fn(async (filter: string) => {
+      // Capture the filter for testing
+      if (collectionName === "dailyLogs") {
+        lastDailyLogFilter = filter;
+      }
       if (!currentMockDailyLog) {
         const error = new Error("No DailyLog found");
         (error as { status?: number }).status = 404;
@@ -100,6 +107,7 @@ describe("GET /api/today", () => {
     vi.clearAllMocks();
     currentMockUser = null;
     currentMockDailyLog = null;
+    lastDailyLogFilter = null;
     // Mock current date to 2025-01-10 for predictable testing
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2025-01-10T12:00:00Z"));
@@ -508,6 +516,24 @@ describe("GET /api/today", () => {
     });
   });
 
+  describe("dailyLog query", () => {
+    it("queries dailyLogs with YYYY-MM-DD date format using contains operator", async () => {
+      // PocketBase filters don't accept ISO format with T separator
+      // Must use simple YYYY-MM-DD with ~ contains operator
+      currentMockUser = createMockUser();
+      currentMockDailyLog = createMockDailyLog();
+
+      await GET(mockRequest);
+
+      // Verify filter uses YYYY-MM-DD format (2025-01-10) not ISO format
+      // The filter should use ~ contains operator, not >= range
+      expect(lastDailyLogFilter).toBeDefined();
+      expect(lastDailyLogFilter).toContain('date~"2025-01-10"');
+      // Should NOT contain ISO format with T separator
+      expect(lastDailyLogFilter).not.toContain("T");
+    });
+  });
+
   describe("biometrics data", () => {
     it("returns biometrics from daily log when available", async () => {
       currentMockUser = createMockUser();