SimurgArray: master plan, repo scaffolding and data/ref fetch scripts

Phase 0 deliverables: full technical specification and roadmap
(SIMURGARRAY_MASTER_PLAN.md), bootstrap script for reference
open-source repos and tiered dataset fetch script with checksums.

.gitignore

@@ -0,0 +1,18 @@
+# vendor / large data — never commit
+data/
+refs/
+_phase0_archive/
+*.idat
+*.idat.gz
+*.bpm
+*.egt
+*.gtc
+# python
+__pycache__/
+.venv/
+*.egg-info/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+# rust
+target/