Add new PNG images for clean and preview outputs

- Added `image_clean.png` to the output directory for the clean image representation.
- Added `image_clean_preview.png` for the preview of the clean image.
- Introduced `image_svg_clean.png` for the SVG clean image representation.

runtime_paths.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+import os
+import shutil
+from pathlib import Path
+
+
+PROJECT_ROOT = Path(__file__).resolve().parent
+DEFAULT_PROFILE_DATA = '{\n  "profiles": {},\n  "active_profile": null\n}\n'
+
+
+def bundle_path(*parts: str) -> Path:
+    base = Path(os.environ.get("MICE_PROJECT_ROOT", PROJECT_ROOT)).expanduser()
+    return base.joinpath(*parts)
+
+
+def resolve_bundle_path(path_like: str | Path) -> Path:
+    candidate = Path(path_like).expanduser()
+    if candidate.is_absolute():
+        return candidate
+    return bundle_path(*candidate.parts)
+
+
+def data_root() -> Path:
+    override = os.environ.get("MICE_DATA_DIR")
+    if override:
+        root = Path(override).expanduser()
+    else:
+        xdg_data_home = Path(os.environ.get("XDG_DATA_HOME", Path.home() / ".local" / "share"))
+        root = xdg_data_home / "mice"
+    root.mkdir(parents=True, exist_ok=True)
+    return root
+
+
+def persistent_data_path(
+    path_like: str | Path,
+    *,
+    default_source: str | Path | None = None,
+    default_text: str = "",
+) -> Path:
+    candidate = Path(path_like).expanduser()
+    if candidate.is_absolute():
+        target = candidate
+    else:
+        target = data_root().joinpath(*candidate.parts)
+
+    target.parent.mkdir(parents=True, exist_ok=True)
+    if target.exists():
+        return target
+
+    if default_source is not None:
+        source = resolve_bundle_path(default_source)
+        if source.exists() and source != target:
+            shutil.copy2(source, target)
+            return target
+
+    target.write_text(default_text, encoding="utf-8")
+    return target