refactor: split monolithic state into context-based modules

Extract image, desktop, mobile, and config state into separate context
providers to improve modularity and reduce unnecessary re-renders.

Signed-off-by: Sped0n <hi@sped0n.com>

assets/ts/mobile/galleryUtils.ts

@@ -0,0 +1,26 @@
+import { type Swiper } from 'swiper'
+
+import type { Vector } from '../utils'
+
+export async function loadSwiper(): Promise<typeof Swiper> {
+  const swiper = await import('swiper')
+  return swiper.Swiper
+}
+
+export function getActiveImageIndexes(
+  currentIndex: number,
+  length: number,
+  navigateVector: Vector
+): number[] {
+  const nextIndex = Math.min(currentIndex + 1, length - 1)
+  const prevIndex = Math.max(currentIndex - 1, 0)
+
+  switch (navigateVector) {
+    case 'next':
+      return [nextIndex]
+    case 'prev':
+      return [prevIndex]
+    case 'none':
+      return [currentIndex, nextIndex, prevIndex]
+  }
+}