fix(FR-441): unexpected disabled download button

[yomybaby]

Resolves #3069 (FR-441)

Fixes file list grid cache refresh issue in folder explorer

Changes:

• Makes _unionedAllowedPermissionByVolume property accessible to child components
• Adds cache clearing after file list grid updates to ensure UI reflects latest changes

** How to reproduce
If you want to simulate race condition to reproduce bug, add a test promise to here like below:

const [vhostInfo, currentKeypairResourcePolicy] = await Promise.all([
      globalThis.backendaiclient.vfolder.list_hosts(),
      this._getCurrentKeypairResourcePolicy(),
      new Promise((resolve)=>{
        setTimeout(()=>{
          resolve(undefined);
        },5000);
      })
    ]);

Test Steps:

1. Navigate to folder explorer
2. Ensure Download button enabled when user had download permission

[yomybaby]

• fix(FR-441): unexpected disabled download button #3069 👈 (View in Graphite)
• main

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[lizable]

Works fine. LGTM.