kit/sync-modules fails without id_rsa, and fails with a different error after I create it or set id_ed25519

I use ed25519 instead of rsa, so when I try to dync modules:

```
user> (kit/sync-modules)
failed to clone module: git@github.com:kit-clj/modules.git
cause: git@github.com:kit-clj/modules.git: java.io.FileNotFoundException: /Users/xxx/.ssh/id_rsa (No such file or directory)
```

So reading the code I found out about `kit.git-config.edn` where I can give the name of my key, but replacing `id_rsa` with `id_ed25519`, I get:

```
user> (kit/sync-modules)
failed to clone module: git@github.com:kit-clj/modules.git
cause: git@github.com:kit-clj/modules.git: invalid privatekey: [B@4cf19be
```

Start at the kit/sync-modules entry point and inspect the kit.git-config.edn handling for SSH key names. Reproduce the failure with an ed25519 key, then verify that module synchronization succeeds without requiring id_rsa or producing the invalid privatekey error.

Written by the indexing model from the issue text.