feat: add all domain layers (dotfiles, packages, remote, containers)

- Dotfiles: models, module resolution, path resolution, link planning
- Packages: models, catalog parsing, resolution, install/remove planning
- Remote: target parsing, SSH command building
- Containers: image refs, mount resolution, container specs

All domain code is pure functions + frozen dataclasses. 88 tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_domain_remote.py

@@ -0,0 +1,79 @@
+"""Tests for remote domain."""
+
+import pytest
+
+from flow.core.config import TargetConfig
+from flow.core.errors import FlowError
+from flow.domain.remote.models import SSHCommand, Target
+from flow.domain.remote.resolution import (
+    build_ssh_command,
+    list_targets,
+    parse_target,
+    resolve_target,
+    terminfo_fix_command,
+)
+
+
+class TestParseTarget:
+    def test_valid_spec(self):
+        ns, plat = parse_target("personal@orb")
+        assert ns == "personal"
+        assert plat == "orb"
+
+    def test_missing_at_raises(self):
+        with pytest.raises(FlowError):
+            parse_target("invalid")
+
+    def test_empty_parts_raises(self):
+        with pytest.raises(FlowError):
+            parse_target("@orb")
+
+
+class TestResolveTarget:
+    def test_found(self):
+        targets = [TargetConfig(namespace="personal", platform="orb", host="personal.orb")]
+        result = resolve_target("personal@orb", targets)
+        assert result.host == "personal.orb"
+        assert result.label == "personal@orb"
+
+    def test_not_found(self):
+        with pytest.raises(FlowError, match="Unknown target"):
+            resolve_target("missing@host", [])
+
+
+class TestBuildSSHCommand:
+    def test_basic(self):
+        target = Target(namespace="personal", platform="orb", host="personal.orb")
+        cmd = build_ssh_command(target)
+        assert "ssh" in cmd.argv
+        assert "personal.orb" in cmd.argv
+        assert cmd.env["DF_NAMESPACE"] == "personal"
+
+    def test_with_identity(self):
+        target = Target(namespace="work", platform="ec2", host="work.ec2", identity="~/.ssh/id_work")
+        cmd = build_ssh_command(target)
+        assert "-i" in cmd.argv
+        assert "~/.ssh/id_work" in cmd.argv
+
+    def test_with_remote_command(self):
+        target = Target(namespace="p", platform="o", host="h")
+        cmd = build_ssh_command(target, remote_command="ls -la")
+        assert cmd.argv[-1] == "ls -la"
+
+
+class TestListTargets:
+    def test_converts_configs(self):
+        configs = [
+            TargetConfig(namespace="a", platform="b", host="a.b"),
+            TargetConfig(namespace="c", platform="d", host="c.d"),
+        ]
+        targets = list_targets(configs)
+        assert len(targets) == 2
+        assert targets[0].label == "a@b"
+
+
+class TestTerminfoFix:
+    def test_returns_commands(self):
+        cmds = terminfo_fix_command()
+        assert len(cmds) == 2
+        assert "infocmp" in cmds[0]