Refactor school year button and enhance JavaScript bindings

- Updated the button for adding a new school year to have an ID for easier access.
- Changed the way IS_SUPERADMIN is defined to use JSON for better compatibility.
- Added event bindings for canceling and saving edits for schools in the JavaScript code.
- Introduced a new document for Google SSO instructions.

.env.example

@@ -27,6 +27,14 @@ BASE_URL=https://leerdoelen.jouwdomain.be
 MICROSOFT_CLIENT_ID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
 MICROSOFT_CLIENT_SECRET=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 
+# ── Google Workspace SSO ───────────────────────────────────────
+# Aanmaken via: https://console.cloud.google.com
+# → APIs & Services → Credentials → OAuth 2.0 Client ID
+# Redirect URI: https://jouwdomain.be/auth/google/callback
+# Zie handleiding: docs/Handleiding_Google_SSO.md
+GOOGLE_CLIENT_ID=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.apps.googleusercontent.com
+GOOGLE_CLIENT_SECRET=GOCSPX-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+
 # Naam van de scholengroep — verschijnt op de loginpagina
 ORG_NAME=GO! Scholengroep 2