* fix: file preview shows stale content when re-opening a file
The file content query inherits `refetchOnMount: false` and
`gcTime: Infinity` from the global QueryClient defaults, so
re-opening a previously viewed file never re-fetches its content.
Set `staleTime: 0` and `refetchOnMount: true` on the file preview
query so it always fetches the latest content when the component
mounts.
Fixes#351
* fix: keep original staleTime, only add refetchOnMount
staleTime: 5_000 is reasonable — avoids redundant fetches when
quickly toggling the same file. The actual fix only needs
refetchOnMount: true to override the global default of false.
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Co-authored-by: muzhi1991 <muzhi1991@limuzhideMac-mini-2.local>