feat: SQLite-backed installations, REST API, admin auth and web UI

Replaces the slice-2 hardcoded installation with a full install/deploy
pipeline:

- SQLite persistence (better-sqlite3) with a single `installations`
  table and a draft -> cloning -> building -> built -> starting ->
  running/error/stopped state machine; env vars and bearer tokens are
  encrypted at rest (AES-256-GCM, key derived from MASTER_KEY).
- Build/run orchestration: git clone (+ .env.example key detection),
  `nixpacks build` as a logged subprocess, dockerode container
  run/stop with forced host/port env vars and a TCP-connect health
  check before flipping an installation to "running".
- REST API (installations CRUD, build/deploy/redeploy, logs, token
  regeneration) behind single-operator session-cookie auth with a
  basic login lockout.
- Vite+React admin SPA: login, installation list, install wizard, and
  a detail page to configure env vars, trigger build/deploy/redeploy,
  view the build log, and copy the authenticated /mcp/<slug> URL.
- Dockerfile (multi-stage, pulls in nixpacks + the Docker CLI) and
  docker-compose.yml for production deployment.

Validated end-to-end against a real cloned repo: draft creation with
env-key detection, build, the error path on a failed health check, and
delete, all through the live API.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.env.example

@@ -8,3 +8,19 @@ DOCKER_SOCKET_PATH=/var/run/docker.sock
 
 # Name of the shared container network joining the manager and every installed MCP container
 MCP_NETWORK_NAME=mcp-net
+
+# Where the manager stores its SQLite DB, cloned repos and build logs
+DATA_DIR=./data
+
+# Public base URL used to build the authenticated MCP links shown in the UI, e.g. https://mcp.example.com
+PUBLIC_BASE_URL=http://localhost:3000
+
+# Password for the single admin/operator account that can use the panel
+ADMIN_PASSWORD=change-me
+
+# Random secret used to sign the admin session cookie
+SESSION_SECRET=change-me-too
+
+# Random string (min 32 chars) used to derive the AES-256-GCM key that encrypts
+# installation env vars and bearer tokens at rest
+MASTER_KEY=change-me-to-a-random-string-of-at-least-32-characters