fix(quality): explicit promise-existence checks + protocol-aware WebDAV URL

SonarCloud new-code findings:
- combo.ts / sync-models route: `if (cachedPromise)` -> `!= null` (intentional
  in-flight-promise reuse; explicit existence check, no behaviour change).
- ObsidianSourceCard WebDAV URL: inherit window.location.protocol instead of
  hard-coding http:// (https when behind a TLS proxy) — clears the http hotspot.

open-sse/services/combo.ts

@@ -1761,7 +1761,7 @@ async function fetchResetAwareQuotaWithCache({
 
   const refresh = () => {
     const existing = resetAwareQuotaCache.get(cacheKey);
-    if (existing?.refreshPromise) return existing.refreshPromise;
+    if (existing?.refreshPromise != null) return existing.refreshPromise;
 
     const refreshPromise = fetcher(connectionId, connection)
       .then((quota) => {

src/app/(dashboard)/dashboard/endpoint/components/ObsidianSourceCard.tsx

@@ -165,10 +165,11 @@ export default function ObsidianSourceCard() {
   };
 
   const getWebdavUrl = (): string => {
-    if (typeof window === "undefined") return "http://<server-ip>/api/v1/webdav/";
-    const host = window.location.hostname;
-    const port = window.location.port;
-    return `http://${host}:${port}/api/v1/webdav`;
+    if (typeof window === "undefined") return "<server-ip>/api/v1/webdav/";
+    // Inherit the page protocol (http on localhost, https behind a TLS proxy)
+    // instead of hard-coding http.
+    const { protocol, hostname, port } = window.location;
+    return `${protocol}//${hostname}:${port}/api/v1/webdav`;
   };
 
   return (

src/app/api/providers/[id]/sync-models/route.ts

@@ -174,7 +174,7 @@ export type EnsureReadyOptions = {
 };
 
 export async function ensureLoopbackServerReady(opts: EnsureReadyOptions = {}): Promise<void> {
-  if (__loopbackReadyPromise) return __loopbackReadyPromise;
+  if (__loopbackReadyPromise != null) return __loopbackReadyPromise;
   __loopbackReadyPromise = (async () => {
     const f = opts.fetch ?? fetch;
     const maxWaitMs = opts.maxWaitMs ?? 30_000;