feat: add mutual pass query with dual-station elevation curve

Port satlover.de dual-station pass matching feature:
- New feature/mutual module with mutual pass data model
- MutualViewModel: compute overlapping passes for two stations
- ElevationCurveChart: Canvas-based dual elevation curve with drag
- MutualScreen: input form + results with expandable cards
- Navigation: add Mutual tab to bottom navigation bar
- i18n: add Chinese/English strings for new feature

settings.gradle.kts

@@ -22,6 +22,7 @@ include(
 )
 include(
     ":feature:map",
+    ":feature:mutual",
     ":feature:passes",
     ":feature:radar",
     ":feature:satellites",