ssh: Introduce LocalHost vs. Remote via Host interface

Motivation: local builds and deployments without ssh

Add a new interface `Host` which is implemented bei either `Remote` or `Localhost`

This simplifies all interactions with hosts. THe caller does ot need to know if the Host is remote or local in mot cases anymore

pkgs/clan-cli/clan_lib/ssh/localhost.py

@@ -0,0 +1,111 @@
+import logging
+import os
+from collections.abc import Iterator
+from contextlib import contextmanager
+from dataclasses import dataclass, field
+
+from clan_lib.cmd import CmdOut, RunOpts, run
+from clan_lib.colors import AnsiColor
+from clan_lib.ssh.host import Host
+
+cmdlog = logging.getLogger(__name__)
+
+
+@dataclass(frozen=True)
+class LocalHost(Host):
+    """
+    A Host implementation that executes commands locally without SSH.
+    """
+
+    command_prefix: str = "localhost"
+    _user: str = field(default_factory=lambda: os.environ.get("USER", "root"))
+    _askpass_path: str | None = None
+
+    @property
+    def target(self) -> str:
+        """Return a descriptive target string for localhost."""
+        return "localhost"
+
+    @property
+    def user(self) -> str:
+        """Return the user for localhost."""
+        return self._user
+
+    def run(
+        self,
+        cmd: list[str],
+        opts: RunOpts | None = None,
+        extra_env: dict[str, str] | None = None,
+        tty: bool = False,
+        verbose_ssh: bool = False,
+        quiet: bool = False,
+        control_master: bool = True,
+    ) -> CmdOut:
+        """
+        Run a command locally instead of via SSH.
+        """
+        if opts is None:
+            opts = RunOpts()
+
+        # Set up environment
+        env = opts.env or os.environ.copy()
+        if extra_env:
+            env.update(extra_env)
+
+        # Handle sudo if needed
+        if self._askpass_path is not None:
+            # Prepend sudo command
+            sudo_cmd = ["sudo", "-A", "--"]
+            cmd = sudo_cmd + cmd
+            env["SUDO_ASKPASS"] = self._askpass_path
+
+        # Set options
+        opts.env = env
+        opts.prefix = opts.prefix or self.command_prefix
+
+        # Log the command
+        displayed_cmd = " ".join(cmd)
+        if not quiet:
+            cmdlog.info(
+                f"$ {displayed_cmd}",
+                extra={
+                    "command_prefix": self.command_prefix,
+                    "color": AnsiColor.GREEN.value,
+                },
+            )
+
+        # Run locally
+        return run(cmd, opts)
+
+    @contextmanager
+    def become_root(self) -> Iterator["LocalHost"]:
+        """
+        Context manager to execute commands as root.
+        """
+        if self._user == "root":
+            yield self
+            return
+
+        # For local execution, we can use sudo with askpass if GUI is available
+        # This is a simplified version - could be enhanced with sudo askpass proxy
+        yield self
+
+    @contextmanager
+    def host_connection(self) -> Iterator["LocalHost"]:
+        """
+        For LocalHost, this is a no-op that just returns self.
+        """
+        yield self
+
+    def nix_ssh_env(
+        self,
+        env: dict[str, str] | None = None,
+        control_master: bool = True,
+    ) -> dict[str, str]:
+        """
+        LocalHost doesn't need SSH environment variables.
+        """
+        if env is None:
+            env = {}
+        # Don't set NIX_SSHOPTS for localhost
+        return env