docs: keep each service README inside its own directory

A service README now describes only its own service: no links to other
services or to the root, and no restating of the shared conventions that
the root README and CLAUDE.md already carry. Each service is a separate
Coolify app on a <service>/** watch path, so a cross-link made editing one
service redeploy another. The rule is recorded at the root; the alloy
compose comment now points at a heading that exists.

README.md

@@ -32,6 +32,11 @@ README.
 Compose names the project after its directory, so `code-server/` comes up as
 the `code-server` project with its own network and volumes.
 
+Each service README covers only its own service. Shared conventions live here
+and are not repeated or linked from a service, so editing one service never
+touches another's directory — each is a separate Coolify app deploying on a
+`<service>/**` watch path.
+
 ## Usage
 
 In Coolify or Dokploy, point a Docker Compose resource at the service directory