Add S-Meter specification and TypeScript interfaces for signal strength conversion (#282)

* Initial plan

* Add S-Meter specification and TypeScript interfaces

Co-authored-by: alexthemitchell <[email protected]>

* Fix PR review comments: correct kCal unit and improve boundary test

Co-authored-by: alexthemitchell <[email protected]>

* Refactor boundary test to avoid tautological condition

Co-authored-by: alexthemitchell <[email protected]>

* Fix K_cal unit labels in documentation - remove incorrect dBm suffix

Co-authored-by: alexthemitchell <[email protected]>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: alexthemitchell <[email protected]>

Author: Copilot