Initial commit: Conflict Checker

Cross-discipline design-contradiction checker for construction drawing
sets. Standalone tool broken out from Iron_Bid; a pipeline stage may
later fold back into Iron_Bid.

Pipeline: PDF->images -> per-sheet assertion extraction -> deterministic
clustering by location -> per-cluster reasoning -> report.
Includes CLI (cli/run_check.py) and web UI (backend/main.py).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

requirements.txt

@@ -0,0 +1,9 @@
+fastapi==0.115.0
+uvicorn[standard]==0.30.6
+python-multipart==0.0.12
+pdf2image==1.17.0
+Pillow==10.4.0
+openai==1.51.0
+httpx==0.27.2          # openai 1.51 passes proxies= to httpx; >=0.28 dropped it
+python-dotenv==1.0.1
+# System dependency (not pip): poppler-utils  -> sudo apt install poppler-utils