fix(amsat): distinguish slots we have no data for from slots nobody reported

Grey meant two different things. The API caps at 500 records however many hours
are requested: measured against the live endpoint, a 72-hour request returned 500
reports spanning only 49 hours, so the oldest 9.5 hours of the third day had no
data at all. Those cells were painted the same grey as "nobody reported", which
claimed knowledge we did not have - 352 of 3168 cells on a real page, a third of
the third day's column.

Slots entirely older than the earliest report in the response now use a lighter
grey. Coverage is judged from all reports rather than per satellite: a quiet
satellite has no reports of its own, but the slots it shares with the rest of the
response were still covered, so it must read as "not heard" rather than "unknown".

The two greys are now in the legend, which previously listed only the four active
states. That matters more than it sounds: on the live page 81% of cells are
"nobody reported" and 11% are outside our data, so a user looking at a mostly-grey
row had no way to tell a dead satellite from a gap in what we fetched. The legend
chips use a solid dot, so the two greys stay distinguishable despite the 25%
alpha background. Strings added to all nine locales.

Three tests cover it: a day entirely before the data starts, a day straddling the
boundary, and an empty response marking nothing as covered.

feature/status/src/main/java/com/rtbishop/look4sat/feature/status/SatStatusScreen.kt

@@ -167,11 +167,16 @@ private fun StatusHeader(fetchedAtUtcMs: Long, isRefreshing: Boolean, onRefresh:
 /** Legend: FlowRow of colored chips — wraps to two lines on narrow screens, stays one line when wide. */
 @Composable
 private fun LegendRow() {
+    // The two greys are listed because most of a typical grid is grey: measured live, 81%
+    // of cells were "nobody reported" and 11% were outside the data we received. Without
+    // the distinction a mostly-grey row reads as a dead satellite.
     val legend = listOf(
         stringResource(id = R.string.amsat_active) to Color(0xFF648FFF),
         stringResource(id = R.string.amsat_tlm) to Color(0xFFFFB000),
         stringResource(id = R.string.amsat_not_heard) to Color(0xFFDC267F),
-        stringResource(id = R.string.amsat_conflict) to Color(0xFFFE6100)
+        stringResource(id = R.string.amsat_conflict) to Color(0xFFFE6100),
+        stringResource(id = R.string.amsat_no_report_legend) to Color(0xFFC0C0C0),
+        stringResource(id = R.string.amsat_no_data_legend) to Color(0xFFE8E8E8)
     )
     FlowRow(
         modifier = Modifier.fillMaxWidth().padding(bottom = 6.dp),