OpenTOPAS-SPECT v0.2.0

Added

• Standard QA phantoms (phantoms/qa/): Jaszczak Deluxe (water cylinder + cold-rod sectors + cold
  spheres for uniformity, resolution, and contrast), the NEMA IEC body phantom (IEC 61675-1 / NEMA NU
  2-2018, six hot fillable spheres in a warm body with a cold foam lung, selectable sphere:background
  ratio), and NEMA NU-1 line/point resolution sources. Geometry is traceable to manufacturer datasheets
  and standards (research/knowledge/spect-qa-phantom-geometry/); no dimension is invented.
• tools/make_qa_phantom.py generates the fragments (Jaszczak model, sphere ratio, with/without scatter).
• examples/qa/ decks imaging each QA phantom through a Symbia LEHR head, and docs/qa_phantoms.md.
• Geometry figures throughout the docs: the collimator hole pattern, the three full-system cameras
  (dual-head, StarGuide, D-SPECT) as OpenTOPAS Qt viewer snapshots, and the Jaszczak / NEMA IEC / patient
  phantoms.
• Contributor guide, code of conduct, security policy, issue and pull-request templates, and a
  .zenodo.json for a citable DOI on release; a runtime-environment section in the installation docs
  (Geant4 data paths and the TOPAS_G4_DATA_DIR pitfall).

Fixed

• D-SPECT full-system geometry corrected to the published specs (Garcia AAPM syllabus; JNMT 2020;48:297;
  JNM 2019;60:1194): nine 40 x 160 mm CZT columns conforming to the left chest, each aimed at the heart
  and fanning ~110 deg, verified collision-free through the swivel.