Feature request: spell check

### Feature summary

Spell check for input

### What problem are you trying to solve?

Spell error in input will be transformed to wrong token cause LLM confusing and more thinking.

### Proposed solution

_No response_

### Workflow impact

_No response_

### Installation context

_No response_

### Additional context

_No response_

No files, tests, or entry points are identified in the issue. First determine which input surfaces are in scope and how spell-check suggestions or corrections should behave, then define tests that establish the expected behavior before implementation.

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