feat: photography features & image optimizations

- Hero carousel: gallery.yaml hero accepts single UUID or array, crossfade component
- Full-bleed single albums: subpages with 1 album skip grid, render photos directly
- EXIF on hover: camera/lens/focal length overlay on grid items (toggle via exifOnHover)
- Customizable grid: columns/gap/aspectRatio/layout (masonry|uniform) via gallery.yaml
- Per-subpage grid overrides: each subpage can override global grid config
- True masonry: per-image aspect ratios from EXIF dimensions
- next/image migration: homepage hero, album covers, grid thumbnails, about portrait
- ThumbHash blur placeholders and dominant color backgrounds
- Custom next/image loader via image proxy with width/quality params
- Lightbox fade-in transition with dominant color background
- Password-protected subpages, health check, rate limiting, OG images

lib/thumbhash.ts

@@ -0,0 +1,42 @@
+/**
+ * ThumbHash utilities for generating blur placeholders and dominant colors.
+ * Uses the thumbhash package to decode Immich's base64-encoded ThumbHash strings
+ * into data URLs and hex color values.
+ */
+
+import { thumbHashToRGBA, thumbHashToDataURL } from 'thumbhash';
+
+/**
+ * Convert an Immich base64-encoded ThumbHash into a tiny data URL
+ * suitable for next/image's blurDataURL prop.
+ */
+export function thumbHashToBlurDataUrl(base64: string): string {
+    const bytes = Uint8Array.from(atob(base64), (c) => c.charCodeAt(0));
+    return thumbHashToDataURL(bytes);
+}
+
+/**
+ * Extract the dominant/average color from a ThumbHash as a hex string.
+ * Computes the weighted average of all non-transparent pixels.
+ */
+export function thumbHashToDominantHex(base64: string): string {
+    const bytes = Uint8Array.from(atob(base64), (c) => c.charCodeAt(0));
+    const { w, h, rgba } = thumbHashToRGBA(bytes);
+
+    let r = 0, g = 0, b = 0, total = 0;
+    for (let i = 0; i < w * h; i++) {
+        const a = rgba[i * 4 + 3];
+        if (a > 0) {
+            const weight = a / 255;
+            r += rgba[i * 4] * weight;
+            g += rgba[i * 4 + 1] * weight;
+            b += rgba[i * 4 + 2] * weight;
+            total += weight;
+        }
+    }
+
+    if (total === 0) return '#888888';
+
+    const avg = (v: number) => Math.round(v / total).toString(16).padStart(2, '0');
+    return `#${avg(r)}${avg(g)}${avg(b)}`;
+}