style: restore CSS-only transitions and update config examples

lib/config.ts

@@ -156,6 +156,7 @@ interface SettingsYaml {
   subtitle?: string;
   exifOnHover?: boolean;
   map?: boolean;
+  transitions?: boolean;
   theme?:
     | string
     | {
@@ -258,6 +259,8 @@ export interface AppConfig {
   legal: LegalConfig;
   /** Show the /map page. Default: false. */
   map: boolean;
+  /** Enable page transitions between routes. Default: true. */
+  transitions: boolean;
   /** Explicit album name overrides from gallery.yaml. */
   albumOverrides: Record<string, string>;
   cacheTtl: number;
@@ -502,6 +505,7 @@ export function getConfig(): AppConfig {
       extraInfo: settings.legal?.extraInfo,
     },
     map: settings.map === true,
+    transitions: settings.transitions !== false,
     albumOverrides,
     cacheTtl: env.CACHE_TTL * 1000,
     rateLimitRpm: env.RATE_LIMIT_RPM,