fix(workflow): cleanup invalid edges/mappings when ports are renamed

[krishna9358]

Summary

Issue
Renaming inputs on an Entry Point node broke validation. While the connection arrow visually disappeared, the underlying graph kept references to the old port ID, causing "Source port not found" errors when saving.

Solution
Updated the canvas logic to detect dynamic port changes. It now automatically removes invalid edges and cleans up stale input mappings on downstream nodes whenever a port is renamed or removed.

File Changes
frontend/src/components/workflow/Canvas.tsx : Added edge validation and cleanup logic to handleUpdateNode.

Testing

• bun run test
• bun run lint
• bun run typecheck
• Additional notes:

Documentation

• Updated the relevant doc(s) (see docs/guide.md) or checked that no updates are needed.
• Recorded contract/architecture changes in both public docs and .ai logs when applicable.

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