Remove sample identities from the repository; document the rule

Datasets may be confidential; sample names and measured unit cells committed to
the repo can leak outside the group working on them. Scrub existing occurrences
and add a "No sample identities in the repository" section to CLAUDE.md
(forbidden: sample/dataset names, internal codes, measured cells tied to a
sample; fine: space group / lattice / twinning descriptors).

- Comments: replace internal dataset codes and protein names with the
  crystallographic situation they illustrate (centred vs pseudo-symmetric,
  holohedral, cubic, F-cubic/hexagonal, ...).
- Docs: same, in the analysis/writer/stream references and example configs.
- Tests: rename sample-named identifiers, TEST_CASE names, file prefixes and
  asserted labels to neutral crystallographic names (e.g. tetragonal_uc);
  behaviour unchanged. Reduce the CrystFEL reference PDB to a bare CRYST1 cell
  file (cell.pdb) and rename the reference data file.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_data/jfjoch_broker_test.py

@@ -17,10 +17,10 @@ start_input = {
     "beam_y_pxl":1136,
     "detector_distance_mm":75, 
     "incident_energy_keV":12.4,
-    "sample_name":"lyso", 
+    "sample_name":"test_sample",
     "unit_cell":{"a":36.9, "b":78.95, "c":78.95, "alpha":90, "beta":90, "gamma":90}, 
     "images_per_trigger":18,
-    "file_prefix":"lyso_test_grid",
+    "file_prefix":"test_grid",
     "grid_scan": {
 	"n_fast":3,
         "step_x_um": 5.0,