Keep the band when the frequency is past the edge

Contest operating goes outside the band edges. Someone answers a CQ at 14352, or
a radio reports a frequency a few hundred hertz off, and Bands.ForFrequency
returned null: the contact scored nothing, missed the per-band dupe check and
exported with no band.

N1MM buckets a frequency by its whole megahertz — its BandFor divides the
kilohertz by 1000 and switches on the result, with 1 and 2 both 160M, 3 and 4
both 80M, 28 and 29 both 10M — and never looks at a band edge. Same rule here,
except that the real edges are checked first: 2190M and 630M are both under
1 MHz and share the bucket, so nothing else can tell them apart. A frequency
under 1 MHz that misses both edge ranges still has no band, as it does in N1MM.

The bandmap clamped its slice to the band edges, so a radio past the edge left
the receiver bar off the top of the scale. The slice now stretches to wherever
the radio is.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/Nonemm.Core.Tests/BandsTests.cs

@@ -18,6 +18,30 @@ public class BandsTests
     public void FrequencyOutsideEveryAllocationHasNoBand() =>
         Assert.Null(Bands.ForFrequency(Frequency.FromKilohertz(12000)));
 
+    /// N1MM buckets by whole megahertz, so a contact made past the edge keeps
+    /// its band instead of losing it.
+    [Theory]
+    [InlineData(14400, "20M")]
+    [InlineData(7305, "40M")]
+    [InlineData(1999.9, "160M")]
+    [InlineData(4100, "80M")]
+    [InlineData(29800, "10M")]
+    [InlineData(21500, "15M")]
+    public void FrequencyPastTheBandEdgeStillCountsAsThatBand(double kilohertz, string expected) =>
+        Assert.Equal(expected, Bands.ForFrequency(Frequency.FromKilohertz(kilohertz))?.Name);
+
+    /// Below 1 MHz every band shares the same megahertz, so only the real edges
+    /// decide.
+    [Theory]
+    [InlineData(137, "2190M")]
+    [InlineData(475, "630M")]
+    public void TheLowFrequencyBandsGoByTheirEdges(double kilohertz, string expected) =>
+        Assert.Equal(expected, Bands.ForFrequency(Frequency.FromKilohertz(kilohertz))?.Name);
+
+    [Fact]
+    public void BroadcastFrequenciesBelowOneMegahertzHaveNoBand() =>
+        Assert.Null(Bands.ForFrequency(Frequency.FromKilohertz(900)));
+
     [Fact]
     public void BandEdgesAreIncluded()
     {