Fix navigation drawer not switching screens on first launch

[richterrene]

What

Fixes the first-launch bug where the navigation drawer opens but tapping a menu entry (Chat / Rules / Settings / About) does not switch screens — the app stays on Map until it is force-stopped and relaunched.

Fixes #373.

Root cause

activity_main.xml gave DrawerLayout two content children plus the drawer:

DrawerLayout
 ├─ CoordinatorLayout   (content_frame + toolbar)   ← content child #1
 ├─ NavigationView      (layout_gravity="start")      ← drawer
 └─ LinearLayout @+id/introduction_view               ← content child #2 (no layout_gravity)

introduction_view is a full-screen, clickable/focusable view with no layout_gravity, so DrawerLayout treats it as a second content view. It is only shown on first launch (until the privacy policy is accepted) and then hidden. Showing then hiding that extra content child leaves DrawerLayout's touch handling broken for the session: taps on NavigationView rows are swallowed as a "close drawer" gesture, so onNavigationItemSelected never fires. A restart recreates the hierarchy cleanly and the overlay is never shown again, which is why a restart "fixes" it.

Fix

Wrap the content and the intro overlay in a single FrameLayout so DrawerLayout has exactly one content child plus the NavigationView drawer. Layout-only change — no Java changes.

Testing

Verified on a Pixel emulator (API 36) against master:

	Tap Chat on first launch
Before	drawer closes, stays on Map; onNavigationItemSelected never fires
After	navigates to ChatFragment; Rules/Settings also verified

Confirmed via dumpsys activity top (fragment swap) and instrumented onNavigationItemSelected / onDrawerClosed / navigateTo logging on both first-launch and post-restart paths.

Note

A Kotlin/Compose rewrite exists on migrate_to_kotlin_and_compose, but master still ships this Java/XML screen, so this targets master. If the Compose UI replaces this screen, the same "single content child under the drawer" rule should carry over.

[cbalster]

Hi @richterrene,
lgtm - thank you very much :)

[stephanlindauer]

Merci @richterrene!