Initial commit: StackPilot Phase 1 (Core)

Self-hosted Docker Compose manager.
- Backend: FastAPI + docker-py + SQLite (JWT auth, file-first stacks,
  lifecycle, live status, WebSocket logs, docker-run converter, audit log)
- Frontend: React + Vite + Tailwind (login/setup, dashboard, stacks,
  stack detail, Monaco editor, dark/light theme)
- Deployment: docker-compose.yml, Dockerfiles, nginx reverse proxy

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

.env.example

@@ -0,0 +1,11 @@
+# Required: a long random secret for signing JWTs.
+# Generate with:  openssl rand -base64 48
+SECRET_KEY=change-me-to-a-long-random-string
+
+# Host directory where stack folders (compose.yaml + .env) are stored.
+# This MUST be the same path on the host and is bind-mounted into the backend.
+STACKS_HOST_DIR=./data/stacks
+
+# Allowed CORS origin(s) for the API (comma separated). The bundled frontend
+# proxies /api, so this only matters if you call the API from another origin.
+CORS_ORIGINS=http://localhost:5009