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/build.gradle.kts

@@ -38,10 +38,12 @@ dependencies {
     implementation(libs.material)
     implementation(libs.activity)
     implementation(libs.constraintlayout)
+    implementation(libs.preference)
     testImplementation(libs.junit)
     androidTestImplementation(libs.ext.junit)
     androidTestImplementation(libs.espresso.core)
     implementation(libs.glide)
     implementation(libs.room.runtime)
     annotationProcessor(libs.room.compiler)
+    implementation(libs.preferences)
 }