Fix #673: Make copied template files writable for immutable distros

On NixOS and other immutable distributions, package files in the store are
read-only. shutil.copytree preserves source permissions, so copied template
files remain read-only. This causes PermissionError when create-theme tries
to write __init__.py into the copied directory.

Added make_tree_writable() that adds user-write permission to all files and
directories after copying. Called automatically by copy_templates().

src/rendercv/cli/copy_templates.py

@@ -1,5 +1,7 @@
+import os
 import pathlib
 import shutil
+import stat
 from typing import Literal
 
 
@@ -29,3 +31,23 @@ def copy_templates(
         copy_templates_to,
         ignore=shutil.ignore_patterns("__init__.py", "__pycache__"),
     )
+    make_tree_writable(copy_templates_to)
+
+
+def make_tree_writable(path: pathlib.Path) -> None:
+    """Add user-write permission to all files and directories in a tree.
+
+    Why:
+        On immutable distributions like NixOS, package files are read-only.
+        shutil.copytree preserves source permissions, so copied files remain
+        read-only. Users need write access to customize templates.
+
+    Args:
+        path: Root directory to make writable.
+    """
+    for dirpath, _, filenames in os.walk(path):
+        dp = pathlib.Path(dirpath)
+        dp.chmod(dp.stat().st_mode | stat.S_IWUSR)
+        for filename in filenames:
+            fp = dp / filename
+            fp.chmod(fp.stat().st_mode | stat.S_IWUSR)

tests/cli/test_copy_templates.py

@@ -1,6 +1,10 @@
+import os
+import pathlib
+import stat
+
 import pytest
 
-from rendercv.cli.copy_templates import copy_templates
+from rendercv.cli.copy_templates import copy_templates, make_tree_writable
 
 
 @pytest.mark.parametrize("template_type", ["markdown", "typst"])
@@ -14,3 +18,42 @@ def test_copy_templates(template_type, tmp_path):
     assert not (destination / "__pycache__").exists()
     # Check that at least some files were copied
     assert any(destination.iterdir())
+
+
+def test_copy_templates_produces_writable_files(tmp_path):
+    destination = tmp_path / "templates"
+
+    copy_templates("typst", destination)
+
+    for dirpath, _, filenames in os.walk(destination):
+        dp = pathlib.Path(dirpath)
+        assert dp.stat().st_mode & stat.S_IWUSR, f"Directory {dp} is not user-writable"
+        for filename in filenames:
+            fp = dp / filename
+            assert fp.stat().st_mode & stat.S_IWUSR, f"File {fp} is not user-writable"
+
+
+def test_make_tree_writable(tmp_path):
+    # Create a tree with read-only files and directories
+    subdir = tmp_path / "readonly_dir"
+    subdir.mkdir()
+    test_file = subdir / "test.txt"
+    test_file.write_text("content")
+    nested = subdir / "nested"
+    nested.mkdir()
+    nested_file = nested / "nested.txt"
+    nested_file.write_text("nested content")
+
+    # Make everything read-only
+    nested_file.chmod(stat.S_IRUSR | stat.S_IRGRP | stat.S_IROTH)
+    nested.chmod(stat.S_IRUSR | stat.S_IXUSR | stat.S_IRGRP | stat.S_IROTH)
+    test_file.chmod(stat.S_IRUSR | stat.S_IRGRP | stat.S_IROTH)
+    subdir.chmod(stat.S_IRUSR | stat.S_IXUSR | stat.S_IRGRP | stat.S_IROTH)
+
+    make_tree_writable(subdir)
+
+    # All should be user-writable now
+    assert subdir.stat().st_mode & stat.S_IWUSR
+    assert test_file.stat().st_mode & stat.S_IWUSR
+    assert nested.stat().st_mode & stat.S_IWUSR
+    assert nested_file.stat().st_mode & stat.S_IWUSR