* refactor(installer): split implementation into sourced modules
* test(installer): harden module path coverage
* fix(installer): qualify interactive privacy and engine claims
The guided installer overstated local-only privacy and ranked
whisper.cpp without evidence. Match PRODUCT.md: on-device local
engines, optional Remote API, and the ~33 language catalog plus
Auto-detect.
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Co-authored-by: Jatin K Malik <jatinkrmalik@gmail.com>