feat(external-editor): Add TextEditorConfig and ExternalEditorConfig models

- Add TextEditorConfig and ExternalEditorConfig dataclasses to models.py
- Create src/external_editor.py with ExternalEditorLauncher class
- Add tests for configuration and launcher functionality
- Support for config.toml [tools.text_editors] and manual_slop.toml default_editor

src/external_editor.py

@@ -0,0 +1,76 @@
+"""External Editor Launcher - Opens files in external text editors for diff viewing."""
+from __future__ import annotations
+
+import subprocess
+import tempfile
+from pathlib import Path
+from typing import Optional, List
+
+from src.models import ExternalEditorConfig, TextEditorConfig
+
+
+class ExternalEditorLauncher:
+    def __init__(self, config: ExternalEditorConfig):
+        self.config = config
+
+    def get_editor(self, editor_name: Optional[str] = None) -> Optional[TextEditorConfig]:
+        if editor_name:
+            return self.config.editors.get(editor_name)
+        return self.config.get_default()
+
+    def build_diff_command(
+        self, editor: TextEditorConfig, original_path: str, modified_path: str
+    ) -> List[str]:
+        cmd = [editor.path] + editor.diff_args + [original_path, modified_path]
+        return cmd
+
+    def launch_diff(
+        self, editor_name: Optional[str], original_path: str, modified_path: str
+    ) -> Optional[subprocess.Popen]:
+        editor = self.get_editor(editor_name)
+        if not editor:
+            return None
+        cmd = self.build_diff_command(editor, original_path, modified_path)
+        try:
+            return subprocess.Popen(cmd)
+        except FileNotFoundError:
+            return None
+
+    def launch_editor(self, editor_name: Optional[str], file_path: str) -> Optional[subprocess.Popen]:
+        editor = self.get_editor(editor_name)
+        if not editor:
+            return None
+        try:
+            return subprocess.Popen([editor.path, file_path])
+        except FileNotFoundError:
+            return None
+
+
+def get_default_launcher() -> ExternalEditorLauncher:
+    from src import models
+    config = models.load_config()
+    editors_config = config.get("tools", {}).get("text_editors", {})
+    default_editor = config.get("tools", {}).get("default_editor")
+    ext_config = ExternalEditorConfig.from_dict({
+        "editors": editors_config,
+        "default_editor": default_editor,
+    })
+    return ExternalEditorLauncher(ext_config)
+
+
+def resolve_project_editor_override(project_path: Optional[str]) -> Optional[str]:
+    if not project_path:
+        return None
+    from src import models
+    try:
+        proj = models.load_project(project_path)
+        return proj.get("default_editor")
+    except Exception:
+        return None
+
+
+def create_temp_modified_file(content: str) -> str:
+    with tempfile.NamedTemporaryFile(mode="w", suffix="_modified", delete=False, encoding="utf-8") as f:
+        f.write(content)
+        return f.name
+pass