sign-manifest: derive ZIP filename from manifest URL, tolerant fallback

Previously the script assumed every ZIP was named proserve-{version}.zip.
That broke when an upload was named "Proserve v1.4.6.zip" (with space and
capital P, the natural name produced by Compress-Archive on a Proserve
v1.4.6/ folder).

Now the script:
1. Reads download.url from each version entry, takes basename().
2. If that exact file is missing, falls back to a glob *{version}*.zip
   in builds/ — succeeds if exactly one match.
3. Logs a clear message in either case.

Also fix manifest example hostname (www.exemple-asterion.com → asterionvr.com).

server/manifest/versions.json

@@ -11,11 +11,11 @@
       "executable": "PROSERVE_UE_5_5.exe",
       "installFolderTemplate": "Proserve v{version}",
       "download": {
-        "url": "https://www.exemple-asterion.com/PS_Launcher/builds/proserve-1.4.6.zip",
+        "url": "https://asterionvr.com/PS_Launcher/builds/proserve-1.4.6.zip",
         "sizeBytes": 0,
         "sha256": "REPLACE_AFTER_BUILD"
       },
-      "releaseNotesUrl": "https://www.exemple-asterion.com/PS_Launcher/api/releasenotes/1.4.6",
+      "releaseNotesUrl": "https://asterionvr.com/PS_Launcher/api/releasenotes/1.4.6",
       "minLicenseDate": "2025-01-01",
       "availableForDownload": true
     },
@@ -25,11 +25,11 @@
       "executable": "PROSERVE_UE_5_5.exe",
       "installFolderTemplate": "Proserve v{version}",
       "download": {
-        "url": "https://www.exemple-asterion.com/PS_Launcher/builds/proserve-1.4.5.zip",
+        "url": "https://asterionvr.com/PS_Launcher/builds/proserve-1.4.5.zip",
         "sizeBytes": 0,
         "sha256": "REPLACE_AFTER_BUILD"
       },
-      "releaseNotesUrl": "https://www.exemple-asterion.com/PS_Launcher/api/releasenotes/1.4.5",
+      "releaseNotesUrl": "https://asterionvr.com/PS_Launcher/api/releasenotes/1.4.5",
       "minLicenseDate": "2024-06-01",
       "availableForDownload": true
     }