fix(tools): prevent duplicate media delivery from write_file

Tell LLM that auto-delivered files should not be sent again via
message tool, preventing double sends (document + photo) on Telegram.

internal/tools/filesystem_write.go

@@ -173,7 +173,11 @@ func (t *WriteFileTool) Execute(ctx context.Context, args map[string]any) *Resul
 		t.workspaceIntc.AfterWrite(ctx, resolved, "write")
 	}
 
-	result := SilentResult(fmt.Sprintf("File written: %s (%d bytes)", path, len(content)))
+	msg := fmt.Sprintf("File written: %s (%d bytes)", path, len(content))
+	if deliver {
+		msg += ". File will be automatically delivered to the user — do NOT send it again via message tool."
+	}
+	result := SilentResult(msg)
 	result.Deliverable = content
 	if deliver {
 		result.Media = []bus.MediaFile{{Path: resolved}}
@@ -191,7 +195,11 @@ func (t *WriteFileTool) executeInSandbox(ctx context.Context, path, content, san
 		return ErrorResult(fmt.Sprintf("failed to write file: %v", err))
 	}
 
-	result := SilentResult(fmt.Sprintf("File written: %s (%d bytes)", path, len(content)))
+	msg := fmt.Sprintf("File written: %s (%d bytes)", path, len(content))
+	if deliver {
+		msg += ". File will be automatically delivered to the user — do NOT send it again via message tool."
+	}
+	result := SilentResult(msg)
 	result.Deliverable = content
 	if deliver {
 		// Sandbox workspace is bind-mounted — resolve to host path for delivery