gitignore: processing output and the data it came from

The working tree accumulates merged reflection files, models and per-image dumps
while testing, and they sit in the repository root next to the source. They are
user data: a merged .mtz/.cif carries a sample's measured unit cell and its
filename usually carries the sample's name, neither of which may enter this
repository. Only build*/ and python-client/ were ignored, so a `git add -A` would
have picked all of it up - which is exactly what happened while preparing this
branch, caught before the commit was made.

Ignore the file types rather than rely on everyone typing the right paths, and
un-ignore tests/ so checked-in fixtures still work (git add -f for anything else
that genuinely belongs). Also widen the rugnux_vs_xds.py output dir to rugnux_cmp*/,
which is where the ad-hoc comparison runs land.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitignore

@@ -4,5 +4,18 @@ build*/
 python-client/
 openapi-generator-cli.jar
 
-# rugnux_vs_xds.py default output dir
-rugnux_cmp/
+# rugnux_vs_xds.py output dirs (the default, and the ad-hoc ones used when comparing runs)
+rugnux_cmp*/
+
+# Processing output and the data it came from. These are USER DATA: a merged .mtz/.cif or a model
+# carries a sample's measured unit cell, and its filename usually carries the sample's name - neither
+# of which may enter this repository (see CLAUDE.md). They accumulate in the working tree while
+# testing, so keep them un-addable rather than relying on everyone typing the right paths.
+*.mtz
+*.cif
+*.pdb
+*.hkl
+*_image.dat
+
+# Test fixtures are checked in deliberately; add them with an explicit path.
+!tests/**