docs: improve readmes for cmd and template components

cmd/README.md

@@ -1,8 +1,14 @@
 # cmd
 
-Executables live here.
+Application entrypoints.
 
-| binary       | purpose           |
-| ------------ | ----------------- |
-| `cmd/server` | web server        |
-| `cmd/user`   | user creation CLI |
+| binary       | purpose                           |
+| ------------ | --------------------------------- |
+| `cmd/server` | HTTP server and worker processes  |
+| `cmd/user`   | User management CLI               |
+
+## Conventions
+
+- Each subdirectory is a `package main` that compiles to a standalone binary.
+- Shared logic lives in `internal/` or `pkg/`, not in `cmd/`.
+- Configuration is read from environment variables — see each binary's `main.go` for the full list.