feat(react,js): improve ActiveBlock TS type

[VojtechVidra]

Pull request checklist

• Create and update TSDoc and export relevant TypeScript types
• Write test for the new/updated features if possible
• Test manually each SDK for larger UI changes
• Link issue to this PR
• Review docs and add or update as needed

[Copilot]

Pull request overview

This PR updates the shared SDK ActiveBlock TypeScript typing to be more precise (discriminated union by type), and simplifies React’s blockToActiveBlock construction accordingly.

Changes:

• Refactors ActiveBlock from a single interface into a discriminated union with per-variant props types (component, tour-component, survey).
• Improves the TSDoc for tourBlockId and how it should be used for stable rendering keys in tours.
• Removes an unnecessary as ActiveBlock["type"] cast in the React SDK when constructing ActiveBlock.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
workspaces/shared/src/types/active-block.ts	Refactors ActiveBlock typing into a discriminated union and updates tourBlockId documentation.
workspaces/react/src/lib/active-block.ts	Removes a redundant type-cast when mapping a workflow block to an ActiveBlock.

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