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>

.gitignore

@@ -0,0 +1,20 @@
+# Python
+.venv/
+venv/
+__pycache__/
+*.pyc
+*.pyo
+
+# Secrets / env
+.env
+*.env
+backend/.env
+
+# Runtime data & artifacts
+backend/uploads/
+backend/outputs/
+out/
+*.log
+
+# Sample drawing sets (large binaries)
+samples/*.pdf