Sprint 2 head-start: Room persistence, ProgressViewModel, ProgressScreen

- Room DB (ArtLegendDatabase, SessionDao, SessionEntity) wired up
- SessionRepository saves scores and queries last 7 sessions per module
- ProgressViewModel exposes sessions as StateFlow
- ProgressScreen replaced with real bar chart + session history list
- MainActivity now persists each game result to Room on return
- build.gradle.kts + gradle.properties: KSP and Room 2.6.1 added

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

build.gradle.kts

@@ -1,6 +1,7 @@
 buildscript {
     val kotlinVersion: String by project
     val androidGradleVersion: String by project
+    val kspVersion: String by project
 
     repositories {
         mavenCentral()
@@ -10,6 +11,7 @@ buildscript {
     dependencies {
         classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
         classpath("com.android.tools.build:gradle:$androidGradleVersion")
+        classpath("com.google.devtools.ksp:com.google.devtools.ksp.gradle.plugin:$kspVersion")
     }
 }