feat: Binary file hex preview in FileViewer

[mkitti]

Summary

• Adds a hex dump preview for binary files in the FileViewer component, showing the first 512 bytes via an HTTP Range request
• Introduces HexDump.tsx — a new component rendering bytes in classic hexdump format (offset | hex | ASCII, 16 bytes/row)
• Adds useFileBinaryPreviewQuery hook that fetches binary preview bytes using the existing /api/content/ endpoint's Range support
• Updates FileViewer to detect binary files via the existing HEAD request (X-Is-Binary header) and render the hex preview instead of attempting text display
• Simplifies the showJsonToggle condition (no longer needs metadataQuery.isSuccess guard)

Example output for a ZIP file:

Showing first 512 of 1,048,576 bytes

0000:  50 4B 03 04 14 00 00 00  08 00 6E 6F 55 58 00 00  PK........noUX..
0010:  00 00 00 00 00 00 00 00  00 00 09 00 1C 00 68 65  ..............he
0020:  6C 6C 6F 2E 74 78 74 55  54 09 00 03 8C 27 4E 7B  llo.txtUT.....'N{
0030:  8C 27 4E 7B 75 78 0B 00  01 04 E8 03 00 00 04 E8  .'N{ux..........

Test plan

• Open a text file — syntax highlighting renders as before
• Open a binary file (e.g. .h5, .zip, .png) — hex dump preview renders with offset, hex, and ASCII columns
• Verify truncation message appears when file is larger than 512 bytes
• Run pixi run test-frontend — all unit tests pass
• Run pixi run node-check — no TypeScript errors
• Run pixi run node-eslint-check — no ESLint errors

🤖 Generated with Claude Code

[mkitti]

In #308, we removed binary previews completely. This adds a 512-byte preview as a hex display.

Flat binary files are common among many Janelia labs due to their simplicity when acquiring data from custom instrumentation. When I asking around if anyone uses NWB files, which are a form of HDF5 files, I got several responses like the following.

1. "We're not using NWB either, just flat binaries in my lab."
2. "We don’t use NWB nor do we have any clear plans to do so. Like [group leader 1, above] we prefer flat binaries or other simple formats."

The hex display adds some intelligible information about a binary file displayed as hex and is reminiscent of the output of hexdump command line utility. Often this can be used to identify a file since the first few bytes can be used to match a file signature. Additionally, some readable ASCII strings may be present in the few files providing some additional identifying information.