migrate to vercel; bump version

src/lib/themes/engine.ts

@@ -0,0 +1,61 @@
+import { THEMES, DEFAULT_THEME_ID } from "@/lib/themes";
+import { CSS_PROPS } from "@/lib/themes/props";
+import type { Theme } from "@/lib/themes/types";
+
+export function getStoredThemeId(): string {
+  if (typeof window === "undefined") return DEFAULT_THEME_ID;
+  return localStorage.getItem("theme") || DEFAULT_THEME_ID;
+}
+
+export function saveTheme(id: string): void {
+  localStorage.setItem("theme", id);
+}
+
+export function getNextTheme(currentId: string): Theme {
+  const list = Object.values(THEMES);
+  const idx = list.findIndex((t) => t.id === currentId);
+  return list[(idx + 1) % list.length];
+}
+
+/** Sets CSS vars and notifies canvas, but does NOT persist to localStorage. */
+export function previewTheme(id: string): void {
+  const theme = THEMES[id];
+  if (!theme) return;
+
+  const root = document.documentElement;
+  for (const [key, prop] of CSS_PROPS) {
+    root.style.setProperty(prop, theme.colors[key]);
+  }
+
+
+  document.dispatchEvent(new CustomEvent("theme-changed", { detail: { id } }));
+}
+
+export function applyTheme(id: string): void {
+  const theme = THEMES[id];
+  if (!theme) return;
+
+  // Set CSS vars on :root for immediate visual update
+  const root = document.documentElement;
+  for (const [key, prop] of CSS_PROPS) {
+    root.style.setProperty(prop, theme.colors[key]);
+  }
+
+  // Update <style id="theme-vars"> so Astro view transitions don't revert
+  let el = document.getElementById("theme-vars") as HTMLStyleElement | null;
+  if (!el) {
+    el = document.createElement("style");
+    el.id = "theme-vars";
+    document.head.appendChild(el);
+  }
+  let css = ":root{";
+  for (const [key, prop] of CSS_PROPS) {
+    css += `${prop}:${theme.colors[key]};`;
+  }
+  css += "}";
+  el.textContent = css;
+
+  saveTheme(id);
+
+  document.dispatchEvent(new CustomEvent("theme-changed", { detail: { id } }));
+}