feat: enable GA4 tracking

Set the measurement ID that replaces the Universal Analytics property
shut down in 2023, which leaves tracking disabled until now. Update
the README section, which still described the ID as empty.

README.md

@@ -171,6 +171,6 @@ resolved by the SPA as before.
 
 ## Google Analytics
 
-`GOOGLE_ANALYTICS_TRACKING_ID` in `src/config.ts` is empty, which disables
-tracking. Set a GA4 measurement ID (`G-XXXXXXXXXX`) to enable it; the old
-Universal Analytics property was shut down in 2023.
+`GOOGLE_ANALYTICS_TRACKING_ID` in `src/config.ts` carries the GA4 measurement
+ID that replaced the Universal Analytics property shut down in 2023. Emptying
+it disables tracking.

src/config.ts

@@ -1,8 +1,7 @@
 const SITE_TITLE = 'Visiome Platform';
 const SITE_SLOGAN = 'Digital archive for vision science';
-// GA4 measurement ID (G-XXXXXXXXXX); empty disables tracking.
-// The former Universal Analytics property (UA-2787276-1) was shut down in 2023.
-const GOOGLE_ANALYTICS_TRACKING_ID = '';
+// Replaces the Universal Analytics property (UA-2787276-1), shut down in 2023.
+const GOOGLE_ANALYTICS_TRACKING_ID = 'G-94PHTGFJ7S';
 const XOONIPS_ITEMTYPES = ['binder', 'model', 'data', 'stimulus', 'tool', 'presentation', 'paper', 'book', 'url'];
 const PICO_MODULES = ['manual_ja', 'primface'];