fix(config): add alias: infinito for infinito-nexus/core

`pkgmgr install infinito` (and `pkgmgr path infinito`, `pkgmgr version
infinito`, etc.) failed with:

    Identifier 'infinito' did not match any repository in config.

The infinito-nexus/core entry in defaults.yaml had no alias, so the
resolver could only match it via the full id `github.com/infinito-nexus/core`
or the bare repository name `core`. Downstream consumers (the
infinito-nexus-core Dockerfile, roles/sys-cli, roles/web-app-navigator,
and the test-install-pkgmgr CI job) all invoke the short identifier
`infinito` and broke once kpmx 1.15.x was rolled out via the floating
`pkgmgr-<distro>:stable` images.

Registering `alias: infinito` on the entry restores the short identifier
without renaming the repository or touching the consumer side.

src/pkgmgr/config/defaults.yaml

@@ -265,6 +265,7 @@ repositories:
       - 44D8F11FD62F878E
       - B5690EEEBB952194
 - account: infinito-nexus
+  alias: infinito
   provider: github.com
   description: Infinito.nexus streamlines Linux-based system setups and Docker image administration, perfect for servers and PCs. It offers extensive solutions for system initialization, admin tools, backups, monitoring, updates, driver management, security, and VPNs.
   homepage: https://infinito.nexus