Drop the local Postgres/Zitadel/SeaweedFS stack, use shared Infrastructure

This repo ran its own separate copy of Postgres, Zitadel and SeaweedFS,
none of which are actually wired into the Go backend yet (auth and file
storage are still unchecked TODOs in the README). Removed that unused
duplicate stack (deploy/docker-compose.dev.yml, deploy/postgres-init/)
in favor of the shared Infrastructure repo also used by Musify and Ping.

make dev-infra now brings up Infrastructure instead, and backend/.env.example
points at its ports (Postgres on dockermanager_db, Zitadel, SeaweedFS)
as placeholders for when those features are implemented.

README.md

@@ -31,16 +31,17 @@ never reach the browser.
 
 **File storage** (planned): SeaweedFS, S3 compatible.
 
-Everything ships as Docker Compose for local development: Postgres, Zitadel
-and SeaweedFS run as infrastructure while the Go API and the SvelteKit app
-run directly on the host for fast iteration.
+Postgres, Zitadel and SeaweedFS are not run by this repo: they're shared
+infrastructure that lives in the separate `Infrastructure` git repository,
+used by other projects too. This repo has no infrastructure containers of
+its own. The Go API and the SvelteKit app run directly on the host for fast
+iteration.
 
 ## Project layout
 
 ```
 backend/   Go API: HTTP router, config, the Docker connector, SQL migrations
 frontend/  SvelteKit app
-deploy/    docker-compose.dev.yml and Postgres init scripts
 ```
 
 ## Running it locally
@@ -52,20 +53,22 @@ make backend
 make frontend
 ```
 
-That brings up Postgres, Zitadel and SeaweedFS, then starts the API on
-`http://localhost:8090` and the frontend on `http://localhost:5173`. The API
-port is 8090 instead of the usual 8080 because that one is often already
-taken by something else on the same machine.
+`make dev-infra` brings up the shared `Infrastructure` stack (Postgres,
+Zitadel, SeaweedFS). Then `make backend` starts the API on
+`http://localhost:8090` and `make frontend` starts the frontend on
+`http://localhost:5173`. The API port is 8090 instead of the usual 8080
+because that one is often already taken by something else on the same
+machine.
 
 Useful endpoints while developing: `/healthz` and `/api/containers`.
 
 ## Status
 
-- [x] Monorepo layout (`backend/`, `frontend/`, `deploy/`)
+- [x] Monorepo layout (`backend/`, `frontend/`)
 - [x] Go backend: `chi` router, env based config, health check
 - [x] `HostConnector` / `LocalConnector`: container listing via the Docker SDK
 - [x] Frontend consuming `/api/containers`
-- [x] Dev infrastructure with Postgres, Zitadel and SeaweedFS
+- [x] Dev infrastructure (Postgres, Zitadel, SeaweedFS) via the shared `Infrastructure` repo
 - [x] Initial schema (`hosts`, `services`, `audit_log`)
 - [ ] OIDC login against Zitadel (BFF pattern)
 - [ ] Persisting hosts and services through the backend