fix: render 3-digit shorthand label colors instead of falling back to gray

Forgejo validates label colors against both the 6-digit and 3-digit
shorthand forms and only expands the shorthand when a label is written,
so labels created before that normalization can still serve #abc-style
colors through the API. The hex parser hard-required 6 digits, painting
those labels gray with white text regardless of their configured color.

Expand the shorthand the same way Forgejo's NormalizeColor does, share
the parser between the background and the luminance-based text color,
and cover both forms with tests.

Forji/Forji/Views/IssueLabelView.swift

@@ -19,10 +19,7 @@ struct IssueLabelView: View {
     }
 
     private var textColor: Color {
-        let hex = label.color.trimmingCharacters(in: CharacterSet(charactersIn: "#"))
-        guard hex.count == 6,
-              let rgb = UInt64(hex, radix: 16)
-        else {
+        guard let rgb = Color.rgbValue(hex: label.color) else {
             return .white
         }
         let red = Double((rgb >> 16) & 0xFF) / 255.0
@@ -35,10 +32,7 @@ struct IssueLabelView: View {
 
 extension Color {
     init?(hex: String) {
-        let hex = hex.trimmingCharacters(in: CharacterSet(charactersIn: "#"))
-        guard hex.count == 6,
-              let rgb = UInt64(hex, radix: 16)
-        else {
+        guard let rgb = Color.rgbValue(hex: hex) else {
             return nil
         }
         self.init(
@@ -47,6 +41,21 @@ extension Color {
             blue: Double(rgb & 0xFF) / 255.0,
         )
     }
+
+    /// Parses a 6-digit or 3-digit shorthand hex color into its RGB value,
+    /// expanding the shorthand the same way Forgejo normalizes label colors
+    /// (#f00 -> #ff0000). Labels created before Forgejo normalized colors on
+    /// write can still carry the shorthand form.
+    static func rgbValue(hex: String) -> UInt64? {
+        var hex = hex.trimmingCharacters(in: CharacterSet(charactersIn: "#"))
+        if hex.count == 3 {
+            hex = hex.map { "\($0)\($0)" }.joined()
+        }
+        guard hex.count == 6 else {
+            return nil
+        }
+        return UInt64(hex, radix: 16)
+    }
 }
 
 #if DEBUG

Forji/ForjiTests/LabelColorHexTests.swift

@@ -0,0 +1,41 @@
+@testable import Forji
+import SwiftUI
+import Testing
+
+struct LabelColorHexTests {
+    // MARK: - Six-digit colors
+
+    @Test func `six digit hex parses`() {
+        #expect(Color(hex: "#ff0000") != nil)
+        #expect(Color(hex: "00ff00") != nil)
+    }
+
+    @Test func `six digit value matches`() throws {
+        let rgb = try #require(Color.rgbValue(hex: "#3366cc"))
+        #expect(rgb == 0x3366CC)
+    }
+
+    // MARK: - Three-digit shorthand
+
+    @Test func `three digit shorthand parses`() {
+        #expect(Color(hex: "#f00") != nil)
+        #expect(Color(hex: "abc") != nil)
+    }
+
+    @Test func `three digit shorthand expands like six digit`() throws {
+        #expect(Color(hex: "#f00") == Color(hex: "#ff0000"))
+        #expect(Color(hex: "abc") == Color(hex: "aabbcc"))
+        let rgb = try #require(Color.rgbValue(hex: "#f00"))
+        #expect(rgb == 0xFF0000)
+    }
+
+    // MARK: - Invalid input
+
+    @Test func `invalid hex returns nil`() {
+        #expect(Color(hex: "") == nil)
+        #expect(Color(hex: "#ff00") == nil)
+        #expect(Color(hex: "12345") == nil)
+        #expect(Color(hex: "xyzxyz") == nil)
+        #expect(Color(hex: "#xyz") == nil)
+    }
+}