fix(roaming): align grid columns like reference and lift footer

Two remaining proportion issues on the user's device:

1. Right-side gap: the three grid rows used a continuous Row
   (60+200+60dp), leaving ~84px of blank space on the right of the
   screen. The reference app uses a RelativeLayout where the right
   column is pinned to the screen edge and the 20dp gaps sit on both
   sides of the centered middle column. Convert each row to a Box:
   left cell align(CenterStart), middle cell align(Center), right
   cell align(CenterEnd) - pixel-identical to the reference.

2. Footer legibility: the credit line ("制作：US1PM  汉化：BA7LCE")
   had a fixed 15dp height with no bottom margin, so it sat directly
   against the navigation bar and part of the text was hard to read.
   Drop the fixed height and add 10dp bottom padding so the text
   renders fully with breathing room above the nav bar.

Verified: feature + app compile, 11 unit tests pass. Marker lookup,
grid math and GPS logic untouched.

feature/roaming/src/main/java/com/rtbishop/look4sat/feature/roaming/RoamingScreen.kt

@@ -265,18 +265,19 @@ fun RoamingScreen() {
             }
         }
         // relativeLayout: 九宫格, 占满剩余, 底部 15dp
+        // 用 Box 等价 RelativeLayout 布局: 左格贴左 / 中格水平居中 / 右格贴右 (成品 main.xml)
         Column(modifier = Modifier.fillMaxWidth().weight(1f).padding(bottom = 15.dp)) {
             // 行1: relativeLayout5 (上排: 纬度 +1)
-            Row(modifier = Modifier.fillMaxWidth().weight(1f)) {
-                GridCell(text = state.grids[0], modifier = Modifier.width(60.dp).fillMaxHeight())
-                GridCell(text = state.grids[1], modifier = Modifier.width(200.dp).fillMaxHeight())
-                GridCell(text = state.grids[2], modifier = Modifier.width(60.dp).fillMaxHeight())
+            Box(modifier = Modifier.fillMaxWidth().weight(1f)) {
+                GridCell(text = state.grids[0], modifier = Modifier.width(60.dp).fillMaxHeight().align(Alignment.CenterStart))
+                GridCell(text = state.grids[1], modifier = Modifier.width(200.dp).fillMaxHeight().align(Alignment.Center))
+                GridCell(text = state.grids[2], modifier = Modifier.width(60.dp).fillMaxHeight().align(Alignment.CenterEnd))
             }
             // 行2: relativeLayout4, 205dp 高 (中排: 中央)
-            Row(modifier = Modifier.fillMaxWidth().height(205.dp)) {
-                GridCell(text = state.grids[3], modifier = Modifier.width(60.dp).fillMaxHeight())
+            Box(modifier = Modifier.fillMaxWidth().height(205.dp)) {
+                GridCell(text = state.grids[3], modifier = Modifier.width(60.dp).fillMaxHeight().align(Alignment.CenterStart))
                 // 中央列: tv22 (100x80dp centerInParent) 叠在 linearLayout3 (200x200dp) 之上
-                Box(modifier = Modifier.width(200.dp).fillMaxHeight()) {
+                Box(modifier = Modifier.width(200.dp).fillMaxHeight().align(Alignment.Center)) {
                     // linearLayout3: 200x200dp, marginTop 2dp, holo_blue_bright
                     Box(
                         modifier = Modifier
@@ -306,22 +307,22 @@ fun RoamingScreen() {
                             .align(Alignment.Center)
                     )
                 }
-                GridCell(text = state.grids[5], modifier = Modifier.width(60.dp).fillMaxHeight())
+                GridCell(text = state.grids[5], modifier = Modifier.width(60.dp).fillMaxHeight().align(Alignment.CenterEnd))
             }
             // 行3: relativeLayout3 (下排: 纬度 -1)
-            Row(modifier = Modifier.fillMaxWidth().weight(1f)) {
-                GridCell(text = state.grids[6], modifier = Modifier.width(60.dp).fillMaxHeight())
-                GridCell(text = state.grids[7], modifier = Modifier.width(200.dp).fillMaxHeight())
-                GridCell(text = state.grids[8], modifier = Modifier.width(60.dp).fillMaxHeight())
+            Box(modifier = Modifier.fillMaxWidth().weight(1f)) {
+                GridCell(text = state.grids[6], modifier = Modifier.width(60.dp).fillMaxHeight().align(Alignment.CenterStart))
+                GridCell(text = state.grids[7], modifier = Modifier.width(200.dp).fillMaxHeight().align(Alignment.Center))
+                GridCell(text = state.grids[8], modifier = Modifier.width(60.dp).fillMaxHeight().align(Alignment.CenterEnd))
             }
         }
-        // tv4: 底部版权, 10sp 黑, 15dp 高
+        // tv4: 底部版权, 10sp 黑 (往上拉, 底部预留空间避免被导航栏遮挡)
         Text(
             text = "制作：US1PM  汉化：BA7LCE",
             fontSize = 10.sp,
             color = Color.Black,
             textAlign = TextAlign.Center,
-            modifier = Modifier.fillMaxWidth().height(15.dp)
+            modifier = Modifier.fillMaxWidth().padding(bottom = 10.dp)
         )
     }
 }