implement artifact win condition (REQ-WIN-ARTIFACT-COUNT, REQ-WIN-SCREEN)

- Add [artifacts] config section to world.toml with artifact_chance_formula (x = station level) and artifact_win_count
- Roll artifact chance before each schematic drop; on success show 2 schematics + Artifact option instead of 3
- Selecting Artifact increments artifact count; reaching artifact_win_count triggers win screen
- Display "Artifacts: x/y" in header bar via ArtifactCountChangedEvent
- Win screen mirrors game-over screen with "Won!" caption and same Restart/Quit buttons

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DUsFgd2Ga6pmLz8giS8WUn

src/lib/core/SchematicChoiceOption.h

@@ -7,7 +7,8 @@ enum class SchematicType
 {
     Ship,
     Module,
-    Recipe
+    Recipe,
+    Artifact
 };
 
 // One option presented to the player in the schematic choice dialog