Add worktree UI branding

ui/src/lib/worktree-branding.ts

@@ -0,0 +1,65 @@
+export type WorktreeUiBranding = {
+  enabled: true;
+  name: string;
+  color: string;
+  textColor: string;
+};
+
+function readMetaContent(name: string): string | null {
+  if (typeof document === "undefined") return null;
+  const element = document.querySelector(`meta[name="${name}"]`);
+  const content = element?.getAttribute("content")?.trim();
+  return content ? content : null;
+}
+
+function normalizeHexColor(value: string | null): string | null {
+  if (!value) return null;
+  const hex = value.startsWith("#") ? value.slice(1) : value;
+  if (/^[0-9a-fA-F]{3}$/.test(hex)) {
+    return `#${hex.split("").map((char) => `${char}${char}`).join("").toLowerCase()}`;
+  }
+  if (/^[0-9a-fA-F]{6}$/.test(hex)) {
+    return `#${hex.toLowerCase()}`;
+  }
+  return null;
+}
+
+function hexToRgb(color: string): { r: number; g: number; b: number } {
+  const normalized = normalizeHexColor(color) ?? "#000000";
+  return {
+    r: Number.parseInt(normalized.slice(1, 3), 16),
+    g: Number.parseInt(normalized.slice(3, 5), 16),
+    b: Number.parseInt(normalized.slice(5, 7), 16),
+  };
+}
+
+function relativeLuminanceChannel(value: number): number {
+  const normalized = value / 255;
+  return normalized <= 0.03928 ? normalized / 12.92 : ((normalized + 0.055) / 1.055) ** 2.4;
+}
+
+function pickReadableTextColor(background: string): string {
+  const { r, g, b } = hexToRgb(background);
+  const luminance =
+    (0.2126 * relativeLuminanceChannel(r)) +
+    (0.7152 * relativeLuminanceChannel(g)) +
+    (0.0722 * relativeLuminanceChannel(b));
+  const whiteContrast = 1.05 / (luminance + 0.05);
+  const blackContrast = (luminance + 0.05) / 0.05;
+  return whiteContrast >= blackContrast ? "#f8fafc" : "#111827";
+}
+
+export function getWorktreeUiBranding(): WorktreeUiBranding | null {
+  if (readMetaContent("paperclip-worktree-enabled") !== "true") return null;
+
+  const name = readMetaContent("paperclip-worktree-name");
+  const color = normalizeHexColor(readMetaContent("paperclip-worktree-color"));
+  if (!name || !color) return null;
+
+  return {
+    enabled: true,
+    name,
+    color,
+    textColor: normalizeHexColor(readMetaContent("paperclip-worktree-text-color")) ?? pickReadableTextColor(color),
+  };
+}