refactor(installer): split implementation into sourced modules (#862)

* 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.

---------

Co-authored-by: Jatin K Malik <jatinkrmalik@gmail.com>

.github/labeler.yml

@@ -45,6 +45,7 @@ installer:
   - changed-files:
       - any-glob-to-any-file:
           - "install.sh"
+          - "install.d/**/*"
           - "uninstall.sh"
 
 # Icons, sounds, screenshots, promo assets

.github/workflows/unified-pipeline.yml

@@ -48,6 +48,7 @@ jobs:
               # pywhispercpp pin out of install.sh and installs the desktop
               # entry and the icon into the AppDir.
               - 'install.sh'
+              - 'install.d/**'
               - 'vocalinux.desktop'
               - 'resources/**'
               - 'justfile'