fix(customisation-sync): stop truncating entry mtimes to 32 bits

PluginDataExDisplayV2.mtime applied `~~` to the sum of millisecond
timestamps before dividing, which keeps only the low 32 bits. The
freshness chip and "Select All Shiny" then compared wrapped values and
could offer an older copy as newer.

Fixes #1194

src/features/ConfigSync/CmdConfigSync.ts

@@ -368,7 +368,8 @@ export class PluginDataExDisplayV2 {
         return this._version;
     }
     get mtime(): number {
-        return ~~this.files.reduce((a, b) => a + b.mtime, 0) / this.files.length;
+        // Millisecond timestamps exceed 32 bits, so `~~` would wrap them.
+        return Math.floor(this.files.reduce((a, b) => a + b.mtime, 0) / this.files.length);
     }
 }
 export type PluginDataEx = {