chore(layouts): introduce layouts/ directory + src/layouts.py; relocate default layout asset

TIER-2 READ AGENTS.md, conductor/workflow.md, conductor/edit_workflow.md,
  conductor/tier2/githooks/forbidden-files.txt,
  conductor/tracks/tier2_leak_prevention_20260620/spec.md,
  conductor/code_styleguides/data_oriented_design.md,
  conductor/code_styleguides/error_handling.md,
  conductor/code_styleguides/type_aliases.md,
  conductor/product-guidelines.md, conductor/code_styleguides/python.md,
  docs/guide_meta_boundary.md before Phase 1 Task 1.10.

Phase 1 of default_layout_install_20260629:
- tests/artifacts/manualslop_layout_default.ini -> layouts/default.ini
  (git mv preserves history; same content, new parallel-to-themes home)
- src/paths.py: layouts: Path field + SLOP_GLOBAL_LAYOUTS env override
  + get_layouts_dir() accessor (mirror themes at 60/83/150/210+)
- src/layouts.py: new LayoutFile @dataclass(frozen=True, slots=True) +
  load_layouts_from_dir/file + load_layouts_from_disk consumer
  (mirror src/theme_models.py + src/theme_2.py; Result drain per error_handling)
- tests/conftest.py:709: reads from layouts/default.ini

src/paths.py

@@ -58,6 +58,7 @@ class PathsConfig:
  tool_presets:       Path
  personas:           Path
  themes:             Path
+ layouts:            Path
  workspace_profiles: Path
  credentials:        Path
  logs_dir:           Path
@@ -81,6 +82,7 @@ def _default_paths_config() -> PathsConfig:
   tool_presets       = root_dir / "tool_presets.toml",
   personas           = root_dir / "personas.toml",
   themes             = root_dir / "themes",
+  layouts            = root_dir / "layouts",
   workspace_profiles = root_dir / "workspace_profiles.toml",
   credentials        = root_dir / "credentials.toml",
   logs_dir           = root_dir / "logs" / "sessions",
@@ -148,6 +150,7 @@ def initialize_paths(config_path: Optional[Path] = None) -> PathsConfig:
   tool_presets       = _resolve_path("SLOP_GLOBAL_TOOL_PRESETS",  "tool_presets",       root_dir / "tool_presets.toml",       config_path),
   personas           = _resolve_path("SLOP_GLOBAL_PERSONAS",       "personas",           root_dir / "personas.toml",           config_path),
   themes             = _resolve_path("SLOP_GLOBAL_THEMES",         "themes",             root_dir / "themes",                  config_path),
+  layouts            = _resolve_path("SLOP_GLOBAL_LAYOUTS",        "layouts",            root_dir / "layouts",                 config_path),
   workspace_profiles = _resolve_path("SLOP_GLOBAL_WORKSPACE_PROFILES", "workspace_profiles", root_dir / "workspace_profiles.toml", config_path),
   credentials        = _resolve_path("SLOP_CREDENTIALS",           "credentials",        root_dir / "credentials.toml",        config_path),
   logs_dir           = _resolve_path("SLOP_LOGS_DIR",              "logs_dir",           root_dir / "logs" / "sessions",       config_path),
@@ -211,6 +214,11 @@ def get_global_themes_path() -> Path:
  [C: src/theme_2.py:load_themes_from_disk]"""
  return _cfg().themes
 
+def get_layouts_dir() -> Path:
+ """Global layouts directory. Frozen at initialize_paths() time.
+ [C: src/layouts.py:load_layouts_from_disk]"""
+ return _cfg().layouts
+
 def get_project_themes_path(project_root: Path) -> Path:
  """[C: src/theme_2.py:load_themes_from_disk]"""
  return project_root / "project_themes.toml"