fix(ui): prevent duplicate chatflow saves

[luochen211]

Summary

• guard chatflow and Agentflow V2 save handlers while a save request is pending
• disable the canvas save control during create/update requests
• disable the new-chatflow save dialog submit while the request is in flight

Fixes #6502

Tests

• corepack pnpm@10.26.0 exec eslint packages/ui/src/views/canvas/index.jsx packages/ui/src/views/agentflowsv2/Canvas.jsx packages/ui/src/views/canvas/CanvasHeader.jsx packages/ui/src/ui-component/dialog/SaveChatflowDialog.jsx
• corepack pnpm@10.26.0 exec prettier --check packages/ui/src/views/canvas/index.jsx packages/ui/src/views/agentflowsv2/Canvas.jsx packages/ui/src/views/canvas/CanvasHeader.jsx packages/ui/src/ui-component/dialog/SaveChatflowDialog.jsx
• corepack pnpm@10.26.0 --filter flowise-ui run build
• git diff --check

[gemini-code-assist]

Code Review

This pull request introduces mechanisms to prevent duplicate or concurrent saving of chatflows in both the standard Canvas and AgentflowCanvas. It tracks in-flight save requests using a reference (saveInProgressRef) and disables save triggers and buttons across the UI, updating the save button text to "Saving..." during submission. Feedback on these changes suggests also disabling the "Cancel" button in the SaveChatflowDialog while a save is in progress to prevent users from closing the dialog mid-transaction.

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[gemini-code-assist]

While saving is in progress (isSubmitting is true), the Cancel button should also be disabled to prevent the user from closing the dialog or triggering other actions while the transaction is in flight.

Suggested change

	<Button onClick={onCancel}>{dialogProps.cancelButtonName}</Button>
	<Button disabled={isSubmitting} onClick={onCancel}>{dialogProps.cancelButtonName}</Button>

[luochen211]

Addressed the review suggestion by disabling Cancel, Escape, and dialog close while the save request is in progress.