feat: implement comprehensive statistics tracking and refactor checkout engine

BREAKING CHANGE: Database schema updated from v3 to v9 (destructive migration)

Major Features:
- Statistics system: Track player performance (darts, points, matches, double-outs)
- Match state management: ONGOING/COMPLETED/CANCELED with state-based queries
- Settings activity: Day/night mode and standard game mode preferences
- CheckoutEngine refactored to standalone utility class with 1/2/3-dart methods

CheckoutConstants Overhaul:
- Generate all possible double-out combinations (~37,200 routes)
- Intelligent route selection (fewer darts > T20/T19 > higher doubles)
- Store both optimal routes and complete alternatives

GameActivity Enhancements:
- Automatic statistics tracking on turn submission and win
- Career average calculation and database updates
- Fixed race condition with dart value capture

Database Changes:
- Added Statistics entity and StatisticsDao
- Player ID migration: int → long for consistency
- Match entity: added MatchState enum and helper methods
- MatchDao: new state-based query methods

Developer Experience:
- Comprehensive JavaDoc across all new/modified classes
- Test harness for checkout generation validation
- Improved code organization with utils package separation

app/src/main/res/layout/activity_add_player.xml

@@ -3,7 +3,8 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="@color/midnight_black">
+    android:background="@color/surface_primary"
+    android:id="@+id/main">
 
     <ImageView
         android:id="@+id/btnDeletePlayer"