chore: Clean up Ralph agent tracking files

Remove .ralph/ directory files from git tracking.
These are no longer needed as the tool-result-refactor is complete.

Also removes root-level prd.json and progress.txt.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/tools/registry.go

@@ -53,7 +53,7 @@ func (r *ToolRegistry) ExecuteWithContext(ctx context.Context, name string, args
 			map[string]interface{}{
 				"tool": name,
 			})
-		return ErrorResult(fmt.Sprintf("tool '%s' not found", name)).WithError(fmt.Errorf("tool not found"))
+		return ErrorResult(fmt.Sprintf("tool %q not found", name)).WithError(fmt.Errorf("tool not found"))
 	}
 
 	// If tool implements ContextualTool, set context