Phase 7: MIT license, portfolio README, Docker, cross-platform start

- LICENSE: MIT
- README: rewritten as portfolio-grade docs (features with code pointers,
  architecture, Docker/Windows/macOS quick starts, BYO-model table)
- Dockerfile (3-stage: SPA build, pip wheels, slim runtime) + compose with
  a /data volume; .dockerignore keeps secrets and local data out
- database.py: AIDND_DB_PATH env override so deployments can relocate the
  SQLite file; documented in backend/.env.example
- start.sh: macOS/Linux dev script with first-run setup

Verified locally: production SPA build served by the backend (deep links
OK), DB created at the override path. Docker image itself untested here
(Docker not installed); flagged in plan/07.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KFsGHju9szibJJa2YJcdbg

docker-compose.yml

@@ -0,0 +1,11 @@
+services:
+  ai-dnd:
+    build: .
+    ports:
+      - "8000:8000"
+    volumes:
+      - ai-dnd-data:/data
+    restart: unless-stopped
+
+volumes:
+  ai-dnd-data: