Use hex values & add theme_color in manifest.json

It looks like support for hsl color values within the manifest
is limited so we have to convert the colors to hex

internal/glance/utils.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"html/template"
+	"math"
 	"net/http"
 	"net/url"
 	"os"
@@ -182,3 +183,58 @@ func ternary[T any](condition bool, a, b T) T {
 // Having compile time errors about unused variables is cool and all, but I don't want to
 // have to constantly comment out my code while I'm working on it and testing things out
 func ItsUsedTrustMeBro(...any) {}
+
+func hslToHex(h, s, l float64) string {
+	s /= 100.0
+	l /= 100.0
+
+	var r, g, b float64
+
+	if s == 0 {
+		r, g, b = l, l, l
+	} else {
+		hueToRgb := func(p, q, t float64) float64 {
+			if t < 0 {
+				t += 1
+			}
+			if t > 1 {
+				t -= 1
+			}
+			if t < 1.0/6.0 {
+				return p + (q-p)*6.0*t
+			}
+			if t < 1.0/2.0 {
+				return q
+			}
+			if t < 2.0/3.0 {
+				return p + (q-p)*(2.0/3.0-t)*6.0
+			}
+			return p
+		}
+
+		q := 0.0
+		if l < 0.5 {
+			q = l * (1 + s)
+		} else {
+			q = l + s - l*s
+		}
+
+		p := 2*l - q
+
+		h /= 360.0
+
+		r = hueToRgb(p, q, h+1.0/3.0)
+		g = hueToRgb(p, q, h)
+		b = hueToRgb(p, q, h-1.0/3.0)
+	}
+
+	ir := int(math.Round(r * 255.0))
+	ig := int(math.Round(g * 255.0))
+	ib := int(math.Round(b * 255.0))
+
+	ir = int(math.Max(0, math.Min(255, float64(ir))))
+	ig = int(math.Max(0, math.Min(255, float64(ig))))
+	ib = int(math.Max(0, math.Min(255, float64(ib))))
+
+	return fmt.Sprintf("#%02x%02x%02x", ir, ig, ib)
+}