Remove 'json', an 8 MB PostScript file committed by accident in #289 #3144

Noticed while auditing the largest tracked files for #3141.

There is a tracked file at the repo root literally named json. It is not JSON — it is an 8,103,683-byte PostScript document generated by ImageMagick:

$ file json
json: PostScript document text conforming DSC level 3.0, Level 1

$ head -5 json
%!PS-Adobe-3.0
%%Creator: (ImageMagick)
%%Title: (json)
%%CreationDate: (2026-07-22T15:19:04+00:00)
%%BoundingBox: -0 -0 1322 1008

It arrived in 809cef9, "Fix broken OpticalDetector import in galaxyscope.py" (#289) — a change that had nothing to do with images or documents. Near-certainly an ImageMagick invocation that wrote its output to a file named json (a misplaced -format json or a stray redirect) and got swept into the commit.

At 8 MB it is the third-largest tracked file in the repo, behind only the two golden-master fixtures, and larger than every asset in docs/wiki/assets/.

Nothing appears to reference it. Proposed: git rm json. Worth a quick confirmation that no workflow globs the repo root for untyped files before deleting, but this looks like a clean removal. Deliberately not bundled into #3141, which is about diff behaviour rather than repo contents.