auth: use get_default_hermes_root() for shared nous_auth.json path

Replace hardcoded ~/.hermes/shared/ references with
get_default_hermes_root() / 'shared' so the cross-profile Nous auth
store lands in the correct location on every platform:

- Linux/macOS: ~/.hermes/shared/
- native Windows: %LOCALAPPDATA%\hermes\shared- Docker / custom HERMES_HOME: <root>/shared/

Updates _nous_shared_auth_dir(), the pytest seat-belt in
_nous_shared_store_path(), and the auth_add_command comment to match.
Previously Windows installs wrote to ~/.hermes/shared/ even though the
rest of the CLI uses %LOCALAPPDATA%\hermes, so profiles couldn't see
each other's shared credential.

hermes_cli/auth_commands.py

@@ -246,7 +246,7 @@ def auth_add_command(args) -> None:
 
     if provider == "nous":
         # Codex-style auto-import: if a shared Nous credential lives at
-        # ~/.hermes/shared/nous_auth.json (written by any previous
+        # <hermes-root>/shared/nous_auth.json (written by any previous
         # successful login), offer to import it instead of running the
         # full device-code flow. This makes `hermes --profile <name>
         # auth add nous --type oauth` a one-tap operation for users who