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

.dockerignore

@@ -0,0 +1,19 @@
+.git
+.claude
+plan
+*.md
+LICENSE
+start.ps1
+start.sh
+
+# Secrets & local data — never in the image
+*.env
+backend/openrouter_key.env
+*.db
+
+# Build/runtime artifacts rebuilt inside the image
+backend/.venv
+**/__pycache__
+**/*.pyc
+frontend/node_modules
+frontend/dist