WIP: Fix drag-and-drop on Windows

[rly]

Summary

Fixes #180

Problem

Drag-and-drop from Windows Explorer into NWB GUIDE does not work on Windows. This is caused by "requestedExecutionLevel": "requireAdministrator" in the electron-builder config (package.json), which forces the app to always run as Administrator. Windows enforces User Interface Privilege Isolation (UIPI), which blocks drag-and-drop from lower-privilege processes (like Explorer) into higher-privilege processes (the elevated Electron app). macOS has no equivalent restriction, which is why this only affects Windows.

This was identified as the root cause in electron/electron#12460.

Solution

1. Change requestedExecutionLevel from "requireAdministrator" to "asInvoker" so the app runs at the same privilege level as Explorer, allowing drag-and-drop to work.

2. Replace direct os.symlink calls with a create_link helper that gracefully handles the loss of guaranteed admin privileges. The app uses symlinks in two places:

   • Creating a directory symlink from the default conversion output path to a custom output directory (convert_to_nwb)
   • Creating file symlinks to aggregate NWB files into a temp directory for DANDI upload (_aggregate_symlinks_in_new_directory)

   On Windows, symlinks require either Administrator privileges or Developer Mode. Since we no longer guarantee admin, create_link uses the following fallback chain:

   • Try os.symlink — works if the user has Developer Mode enabled or is running as admin
   • Fall back to directory junctions (_winapi.CreateJunction) for directories — these never require admin
   • Fall back to hard links (os.link) for files — these don't require admin but require source and destination to be on the same drive
   • Raise a clear error if all options fail, advising the user to either run NWB GUIDE as Administrator or ensure files are on the same drive

   On non-Windows platforms, behavior is unchanged (always uses os.symlink).

Test plan

• Test drag-and-drop on Windows without running as Administrator
• Test conversion with a custom output directory on Windows
• Test DANDI upload of multiple filesystem objects on Windows
• Test that click-to-choose file selection still works
• Verify no regressions on macOS

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