fix(data): use round(log10(x)) for magnitude notation

The previous formula used floor(log10(x)) which was mathematically
incorrect for magnitude notation. The correct formula is round(log10(x)),
which better represents the order of magnitude by rounding to the nearest
integer power of 10.

This affects several display values:
- ,234.23: 3 → 4
- 00.00: 2 → 3
- 2.00: 1 → 2
- .50: 0 → 1
- .50: -1 → 0
- .00: 0 → 1

closes #175

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: cpcloud

internal/app/mag.go

@@ -64,7 +64,7 @@ func magFormat(c cell, includeUnit bool) string {
 		return fmt.Sprintf("%s%s%s0", sign, unit, magArrow)
 	}
 
-	mag := int(math.Floor(math.Log10(math.Abs(f))))
+	mag := int(math.Round(math.Log10(math.Abs(f))))
 	return fmt.Sprintf("%s%s%s%d", sign, unit, magArrow, mag)
 }
 

internal/app/mag_test.go

@@ -16,11 +16,11 @@ func TestMagFormatMoneyWithUnit(t *testing.T) {
 		value string
 		want  string
 	}{
-		{"thousands", "$5,234.23", "$ \U0001F8213"},
-		{"hundreds", "$500.00", "$ \U0001F8212"},
+		{"thousands", "$5,234.23", "$ \U0001F8214"},
+		{"hundreds", "$500.00", "$ \U0001F8213"},
 		{"millions", "$1,000,000.00", "$ \U0001F8216"},
 		{"zero", "$0.00", "$ \U0001F8210"},
-		{"negative", "-$5.00", "-$ \U0001F8210"},
+		{"negative", "-$5.00", "-$ \U0001F8211"},
 		{"negative large", "-$12,345.00", "-$ \U0001F8214"},
 	}
 	for _, tt := range tests {
@@ -39,14 +39,14 @@ func TestMagFormatBareMoney(t *testing.T) {
 		value string
 		want  string
 	}{
-		{"thousands", "$5,234.23", "\U0001F8213"},
-		{"hundreds", "$500.00", "\U0001F8212"},
+		{"thousands", "$5,234.23", "\U0001F8214"},
+		{"hundreds", "$500.00", "\U0001F8213"},
 		{"millions", "$1,000,000.00", "\U0001F8216"},
-		{"tens", "$42.00", "\U0001F8211"},
-		{"single digit", "$7.50", "\U0001F8210"},
-		{"sub-dollar", "$0.50", "\U0001F821-1"},
+		{"tens", "$42.00", "\U0001F8212"},
+		{"single digit", "$7.50", "\U0001F8211"},
+		{"sub-dollar", "$0.50", "\U0001F8210"},
 		{"zero", "$0.00", "\U0001F8210"},
-		{"negative", "-$5.00", "-\U0001F8210"},
+		{"negative", "-$5.00", "-\U0001F8211"},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -62,7 +62,7 @@ func TestMagFormatDrilldown(t *testing.T) {
 		value string
 		want  string
 	}{
-		{"count", "42", "\U0001F8211"},
+		{"count", "42", "\U0001F8212"},
 		{"zero", "0", "\U0001F8210"},
 		{"large", "1000", "\U0001F8213"},
 	}
@@ -138,7 +138,7 @@ func TestMagTransformCells(t *testing.T) {
 	assert.Equal(t, "Deck", out[1][1].Value)
 
 	// Money cells: magnitude only ($ stripped by transform).
-	assert.Equal(t, "\U0001F8213", out[0][2].Value)
+	assert.Equal(t, "\U0001F8214", out[0][2].Value)
 	assert.Equal(t, "\U0001F8212", out[1][2].Value)
 
 	// Drilldown counts transformed.
@@ -167,8 +167,8 @@ func TestMagModeWorksInEditMode(t *testing.T) {
 }
 
 func TestMagCentsIncludesUnit(t *testing.T) {
-	assert.Equal(t, "$ \U0001F8213", magCents(523423))
-	assert.Equal(t, "$ \U0001F8212", magCents(50000))
+	assert.Equal(t, "$ \U0001F8214", magCents(523423))
+	assert.Equal(t, "$ \U0001F8213", magCents(50000))
 	assert.Equal(t, "$ \U0001F8210", magCents(100))
 }