feat(appearance): left stripe by default, with fill and strength as choices

The first version filled the whole row at 24%, and in a real log that meant
every row was painted: nearly every contact has SOME QSL state, so colour was
present everywhere and stopped being information — a striped background with
the data behind it.

The default is now a 3px stripe down the left edge. Same signal, nothing lost
to read it. A filled row is still offered, with a strength slider, for
operators who want the block — and the rule cards in Settings preview whichever
is chosen, so the decision is made by looking rather than by imagining.

Drawn as an inset shadow rather than a border: a border would shift the cells
three pixels on coloured rows only, and the columns would stop lining up.

Style and strength are normalised rather than rejected — a value out of range
is a slider that got away, not a reason to reset the operator's colours.

appearance_test.go

@@ -49,3 +49,29 @@ func TestRowColorsKeepPriorityOrder(t *testing.T) {
 		t.Errorf("confirmed_lotw lost its colour: %q", got.Rules[0].Color)
 	}
 }
+
+// Style and strength are normalised, not rejected: they only shape a colour, and
+// a value that got away is a slider, not a fault worth resetting the operator's
+// whole choice for.
+func TestRowColorsNormaliseStyleAndIntensity(t *testing.T) {
+	for _, tc := range []struct {
+		inStyle   string
+		inPct     int
+		wantStyle string
+		wantPct   int
+	}{
+		{"bar", 12, "bar", 12},
+		{"tint", 30, "tint", 30},
+		{"both", 45, "both", 45},
+		{"", 0, "bar", 12},           // never configured
+		{"wallpaper", 12, "bar", 12}, // not a style we draw
+		{"tint", 900, "tint", 45},    // clamped, not reset
+		{"tint", -5, "tint", 12},
+	} {
+		got := normRowColors(RowColorSettings{Style: tc.inStyle, Intensity: tc.inPct})
+		if got.Style != tc.wantStyle || got.Intensity != tc.wantPct {
+			t.Errorf("(%q,%d) -> (%q,%d), want (%q,%d)",
+				tc.inStyle, tc.inPct, got.Style, got.Intensity, tc.wantStyle, tc.wantPct)
+		}
+	}
+}