Adds "a stack whose default is a substrate": a shared self-hosted Supabase
backend plus a `--stack supabase` that scaffolds per-app projects (migrations +
edge functions + static UI) which deploy against it. Apps own their code and
stay repo-durable; only their rows/blobs live on the shared substrate.
- compose runner: new RunCompose supervises a multi-container stack as one
systemd unit (ExecStart=`compose up`, generated ExecStop=`compose down`);
secrets via EnvironmentFile. Reusable beyond Supabase. Deployment.stop_cmd
carries the teardown command through the registry.
- supabase stack: CLI --stack choice, STACK_DEFAULTS→frontend with
build.outputs=[public], _scaffold_supabase() (migrations/RLS/functions/
static UI/app manifest), and SupabaseHandler with a forward-only idempotent
migration runner (plan_migrations + psql build) and deno dev-verbs.
- docs: docs/stacks/supabase.md, registered in CLAUDE.md; compose runner
documented in registry.md.
- tests: compose run/stop cmd, systemd ExecStop, compose host-route TLS,
migration planner, supabase verb resolution, create --stack supabase.
