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_dotfiles_models.py

@@ -0,0 +1,47 @@
+"""Tests for dotfiles domain models."""
+
+from pathlib import Path
+
+from flow.domain.dotfiles.models import (
+    LinkOp,
+    LinkPlan,
+    LinkTarget,
+    LinkedState,
+    ModuleRef,
+    Package,
+    PlanSummary,
+)
+
+
+def test_link_op_str_create():
+    op = LinkOp(type="create_link", target=Path("/home/x/.zshrc"),
+                source=Path("/dots/zsh/.zshrc"), package="_shared/zsh", needs_sudo=False)
+    assert "LINK:" in str(op)
+    assert ".zshrc" in str(op)
+
+
+def test_link_op_str_sudo():
+    op = LinkOp(type="create_link", target=Path("/etc/hosts"),
+                source=Path("/dots/dns/hosts"), package="_shared/dns", needs_sudo=True)
+    assert "(sudo)" in str(op)
+
+
+def test_linked_state_roundtrip():
+    lt = LinkTarget(source=Path("/a"), target=Path("/b"), package="p", from_module=False, needs_sudo=False)
+    state = LinkedState(links={Path("/b"): lt})
+    data = state.as_dict()
+    restored = LinkedState.from_dict(data)
+    assert Path("/b") in restored.links
+    assert restored.links[Path("/b")].source == Path("/a")
+    assert restored.links[Path("/b")].package == "p"
+
+
+def test_linked_state_empty():
+    state = LinkedState.from_dict({})
+    assert state.links == {}
+
+
+def test_package_has_id():
+    pkg = Package(name="zsh", layer="_shared", package_id="_shared/zsh",
+                  source_dir=Path("/dots/_shared/zsh"), module=None, local_files=())
+    assert pkg.package_id == "_shared/zsh"