feat: standalone curl-pipe installer, no clone required

- install.sh works outside a checkout: installs into CONTAINR_DIR
  (default ./containr), downloads docker-compose.yml + .env.example from
  the repo, generates secrets, pulls published images
- CONTAINR_REF selects the git ref for downloads; CONTAINR_BUILD=1 or a
  failed pull fetches the source tarball and builds locally
- env-var overrides (HTTP_PORT/API_PORT/...) are persisted into .env;
  health-wait ports resolve env -> .env -> defaults
- drop fixed `name: containr` from root compose so installs in different
  directories get distinct project names
- README: curl one-liner is the primary install path

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

docker-compose.yml

@@ -1,5 +1,3 @@
-name: containr
-
 services:
   postgres:
     image: postgres:15-alpine