Refactor session encryption variable names for consistency

- Changed `NUXT_SESSION_SECRET` to `NUXT_SESSION_PASSWORD` across configuration files and documentation to align with the usage in nuxt-auth-utils.
- Updated related comments and documentation to reflect the new variable name, ensuring clarity for developers and users.

nuxt.config.ts

@@ -69,10 +69,10 @@ export default defineNuxtConfig({
     },
 
     // Session configuration
+    // Note: nuxt-auth-utils automatically reads NUXT_SESSION_PASSWORD from process.env
     session: {
       maxAge: 60 * 60 * 24 * 30, // 30 days in seconds
       name: 'experimenta-session',
-      password: process.env.NUXT_SESSION_SECRET || '',
     },
 
     // Test credentials (for automated testing only)