Fix intensity minutes URL to use path parameters

The Garmin API uses path parameters, not query parameters:
- Correct: /usersummary-service/stats/im/weekly/{start}/{end}
- Wrong: /usersummary-service/stats/im/weekly?start=...&end=...

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

src/lib/garmin.test.ts

@@ -473,7 +473,7 @@ describe("fetchIntensityMinutes", () => {
 
     expect(result).toBe(75);
     expect(global.fetch).toHaveBeenCalledWith(
-      "https://connectapi.garmin.com/usersummary-service/stats/im/weekly?start=2024-01-08&end=2024-01-15",
+      "https://connectapi.garmin.com/usersummary-service/stats/im/weekly/2024-01-08/2024-01-15",
       expect.objectContaining({
         headers: expect.objectContaining({
           Authorization: "Bearer test-token",

src/lib/garmin.ts

@@ -190,7 +190,7 @@ export async function fetchIntensityMinutes(
     const startDate = startDateObj.toISOString().split("T")[0];
 
     const response = await fetch(
-      `${GARMIN_API_URL}/usersummary-service/stats/im/weekly?start=${startDate}&end=${endDate}`,
+      `${GARMIN_API_URL}/usersummary-service/stats/im/weekly/${startDate}/${endDate}`,
       {
         headers: getGarminHeaders(oauth2Token),
       },