ui: SmartTube-style home rows, focus memory and UX-review fixes

The home screen is now stacked horizontal rows ('Continue watching'
with red progress bars from server-reported positions, 'New videos'
paged) instead of one tall list - matching the SmartTube look the app
is modeled on. The player renders as an overlay so the list beneath
keeps its scroll and focus across BACK (was resetting to the top),
grid scroll state is saved per destination, cards render focus
scale/border via tv-material, thumbnails carry relative dates and
privacy badges only where meaningful, overscan margins guard the 1080p
safe area, and the setup screen got a password reveal, clipboard paste
helpers and an always-focusable validating Sign in.

UX review by Claude Opus 5.5 (claude CLI) on emulator screenshots;
remaining suggestions are triaged in BACKLOG.md.

app/build.gradle.kts

@@ -35,6 +35,7 @@ android {
     }
     buildFeatures {
         compose = true
+        buildConfig = true
     }
 }