feat: write the mairie status back to Nextcloud over CalDAV

REPORT by UID gives href + ETag + calendar-data, then PUT with If-Match: the
resource URL is never guessed and a concurrent edit yields 412 instead of an
overwrite. URL_COLLECTION is derived from URL_CALENDRIER.

nextcloud.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, test } from "bun:test";
 import {
   URL_CALENDRIER,
+  URL_COLLECTION,
   recupererFluxCalendrier,
 } from "./extension/nextcloud.js";
 
@@ -64,3 +65,11 @@ describe("recupererFluxCalendrier", () => {
     expect(optionsVues).toEqual({ credentials: "include" });
   });
 });
+
+describe("URL_COLLECTION", () => {
+  test("= URL_CALENDRIER sans ?export, et se termine par /", () => {
+    expect(URL_COLLECTION).toBe(URL_CALENDRIER.replace("?export", ""));
+    expect(URL_COLLECTION.endsWith("/")).toBe(true);
+    expect(URL_COLLECTION).not.toContain("?export");
+  });
+});