Phase 1: FastAPI backend with async job model

- backend/app: FastAPI API wrapping the CAD skill modules
  - upload -> job -> poll -> model / BOM / artifacts -> geometry query
  - SQLite via SQLModel (Model, Job, BomRow, QueryLog)
  - ThreadPoolExecutor worker, serialized, with live stage updates
- docker-compose.yml: dev server (mounts source, --reload) on :8000
- api-test.sh: end-to-end live validation script
- requirements.txt: add fastapi, uvicorn, python-multipart, sqlmodel
- external_diagram.py: port active-area detection OCC.Core -> OCP
- .gitignore, PHASE1.md

Validated live: MR16 round-trip passes (28 BOM rows, 12 artifacts,
bounding-box query, xlsx download; active-area detection working).

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

docker-compose.yml

@@ -0,0 +1,28 @@
+# Dev compose for the Phase 1 API.
+#
+# Mounts the repo into the image and runs uvicorn with --reload, so editing
+# backend/ or skill.src/ takes effect without a rebuild. The image only needs
+# rebuilding when requirements.txt changes (./build.sh).
+#
+#   docker compose up           # http://localhost:8000  (docs at /docs)
+#
+# On Unraid this becomes a real service on br0; for now it's a localhost dev loop.
+services:
+  api:
+    image: step-parser:dev
+    platform: linux/amd64
+    entrypoint: ["uvicorn", "backend.app.main:app", "--host", "0.0.0.0", "--port", "8000", "--reload"]
+    working_dir: /app
+    environment:
+      PYTHONPATH: /app
+      DATA_DIR: /data
+      # ANTHROPIC_API_KEY: set in a .env file (compose reads it automatically) for --translate
+    ports:
+      - "8000:8000"
+    volumes:
+      - ./backend:/app/backend
+      - ./skill.src:/app/skill.src
+      - step_parser_data:/data
+
+volumes:
+  step_parser_data: