fix: resolve 8 bugs affecting real users

- Fix KeyError 'root' in FileGrouper when merging groups with no root-level files
- Fix changelog commit parsing breaking on multiline bodies (use %x00 separator)
- Add empty choices/content checks in OpenAI, Anthropic, OpenRouter providers
- Fix config edit crash when config is empty
- Fix validate command using wrong color for 'no staged files'
- Add type check for corrupted YAML config (non-dict returns empty dict)

devgen/cli/commit.py

@@ -120,7 +120,7 @@ def validate() -> None:
         for f in staged:
             typer.echo(f"- {f}")
     else:
-        typer.secho("[i] No staged files.", fg=typer.colors.RED)
+        typer.secho("[i] No staged files.", fg=typer.colors.YELLOW)
 
 
 @app.command("undo")