Refactor large Kotlin source files

- Split core game models from sandbox engine, native level setup, and repo state saving.

- Move app overlays and completion helpers out of GitHugApp.

- Extract the terminal special key bar into its own component.

app/src/main/java/solutions/tretter/githugandroid/TerminalSpecialKeyBar.kt

@@ -0,0 +1,77 @@
+package solutions.tretter.githugandroid
+
+import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.Button
+import androidx.compose.material3.ButtonDefaults
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+
+@Composable
+internal fun SpecialKeyBar(
+    onTab: () -> Unit,
+    onHelp: () -> Unit,
+    onCursorLeft: () -> Unit,
+    onCursorRight: () -> Unit,
+    onHistoryUp: () -> Unit,
+    onHistoryDown: () -> Unit,
+    onInsertText: (String) -> Unit,
+) {
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .horizontalScroll(rememberScrollState()),
+        horizontalArrangement = Arrangement.spacedBy(1.dp),
+    ) {
+        TerminalKeyButton(label = "?", onClick = onHelp, highlight = true, fontFamily = FontFamily.Default)
+        TerminalKeyButton(label = "↹", onClick = onTab, fontFamily = FontFamily.Default)
+        TerminalKeyButton(label = ".", onClick = { onInsertText(".") })
+        TerminalKeyButton(label = "-", onClick = { onInsertText("-") })
+        TerminalKeyButton(label = "/", onClick = { onInsertText("/") })
+        TerminalKeyButton(label = "←", onClick = onCursorLeft)
+        TerminalKeyButton(label = "→", onClick = onCursorRight)
+        TerminalKeyButton(label = "↑", onClick = onHistoryUp)
+        TerminalKeyButton(label = "↓", onClick = onHistoryDown)
+    }
+}
+
+@Composable
+private fun TerminalKeyButton(
+    label: String,
+    onClick: () -> Unit,
+    highlight: Boolean = false,
+    fontFamily: FontFamily = FontFamily.Monospace,
+) {
+    Button(
+        onClick = onClick,
+        modifier = Modifier
+            .width(32.dp)
+            .height(26.dp),
+        shape = RoundedCornerShape(0.dp),
+        contentPadding = PaddingValues(horizontal = 0.dp, vertical = 0.dp),
+        colors = ButtonDefaults.buttonColors(
+            containerColor = if (highlight) Color(0xFF1976D2) else PanelSecondary,
+            contentColor = TextPrimary,
+        ),
+    ) {
+        Text(
+            text = label,
+            fontFamily = fontFamily,
+            fontWeight = FontWeight.Bold,
+            fontSize = 11.sp,
+        )
+    }
+}