Update Next.js to version 15.4.2 and refactor invoice pages

- Upgrade Next.js and related packages for improved performance and security
- Refactor invoice-related pages to streamline navigation and enhance user experience
- Consolidate invoice editing and viewing functionality into a single page
- Remove deprecated edit page and implement a new view page for invoices
- Update links and routing for consistency across the dashboard

.env.example

@@ -1,23 +1,21 @@
-# Since the ".env" file is gitignored, you can use the ".env.example" file to
-# build a new ".env" file when you clone the repo. Keep this file up-to-date
-# when you add new variables to `.env`.
+# Base application env (example)
+NODE_ENV=production
+PORT=3000
+HOSTNAME=0.0.0.0
 
-# This file will be committed to version control, so make sure not to have any
-# secrets in it. If you are cloning this repo, create a copy of this file named
-# ".env" and populate it with your secrets.
+# NextAuth
+AUTH_SECRET=replace-with-strong-secret
 
-# When adding additional environment variables, the schema in "/src/env.js"
-# should be updated accordingly.
+# Database (Postgres)
+DATABASE_URL=postgres://beenvoice:beenvoice@db:5432/beenvoice
+# Disable SSL for Docker local Postgres; set to false or remove for managed Postgres
+DB_DISABLE_SSL=true
 
-# Next Auth
-# You can generate a new secret on the command line with:
-# npx auth secret
-# https://next-auth.js.org/configuration/options#secret
-AUTH_SECRET=""
+# Email (Resend). Replace with real keys in production
+RESEND_API_KEY=replace-or-remove
+RESEND_DOMAIN=
+
+# Build tweaks
+SKIP_ENV_VALIDATION=1
 
-# Drizzle
-DATABASE_URL="file:./db.sqlite"
 
-# Resend
-RESEND_API_KEY=""
-RESEND_DOMAIN=""