fix(tv): re-enable navigation_home nextFocusRight so D-pad can reach the 'None' provider button

[RjBiermann]

Fixes #2592

Problem

On TV, the D-pad cannot reach the "None" / provider-selector button (home_change_api) on the home screen. After navigating away from Home and back (via Search/Favorites, the BACK button, or even a fresh load), pressing right from the nav rail does nothing — focus is stuck on the rail.

Root cause

onNavDestinationSelected (MainActivity.kt) sets nextFocusRightId on all nav-rail buttons when navigating to Search/Favorites/Downloads (pointing at e.g. main_search), but the navigation_home case was commented out with a stale id. Two problems followed:

1. Returning Home never re-pointed the rail — it stayed aimed at the destroyed Search fragment's main_search, so right-focus from the rail was dead.
2. That hook only fires on rail-button navigation anyway: the BACK-button return path and first app load never ran it at all.

Fix

Move the Home rail-focus handling into addOnDestinationChangedListener (MainActivity.kt), which fires on every arrival at Home regardless of how you got there:

if (navDestination.matchDestination(R.id.navigation_home)) {
    ...
    navRailView.nextFocusRightId = R.id.home_change_api
    // ... and for each nav rail button
}

so on every visit to Home, all rail buttons' nextFocusRightId point at the provider-selector button.

Verification

Reproduced on the TV emulator (blank home, "None" selected) across all three arrival paths:

• Cold start: LEFT → RIGHT returns to "None"
• Search → BACK → Home: RIGHT reaches home_change_api
• Search → rail Home: RIGHT reaches home_change_api

Also verified with a plugin + home content loaded (StreamPlay): LEFT/RIGHT between rail and provider button works, and DOWN from the provider button drops into content as before.

Notes

• The old commented mapping used a stale id (home_preview_change_api); the live id is home_change_api, which exists in both fragment_home.xml and fragment_home_tv.xml.
• Initial focus still lands on the provider button via <requestFocus /> in fragment_home_tv.xml; this change additionally makes the rail→provider path work on every arrival.

AI note: this change was written with AI assistance per AI-POLICY.md; the logic was reproduced and verified on the TV emulator and every line is understood.