fix: Add WAGTAILADMIN_BASE_URL setting to resolve Wagtail warning

Add WAGTAILADMIN_BASE_URL setting to all Django settings files to fix
the wagtailadmin.W003 warning that appeared during system checks.

The project had a BASE_URL setting but Wagtail expects the setting to
be named WAGTAILADMIN_BASE_URL for admin URLs outside the admin interface.

Changes:
- base.py: Set WAGTAILADMIN_BASE_URL = BASE_URL (https://python.ie)
- tests.py: Override with http://testserver for test environment
- dev.py: Override with http://localhost:8000 for local development

This ensures admin URLs in notification emails and the user bar will
display correctly in all environments.

Fixes #175

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: matrixise

pythonie/pythonie/settings/base.py

@@ -34,6 +34,10 @@
 # e.g. in notification emails. Don't include '/admin' or a trailing slash
 BASE_URL = "https://python.ie"
 
+# Wagtail admin base URL for admin URLs outside the admin interface
+# (e.g. notification emails and the user bar)
+WAGTAILADMIN_BASE_URL = BASE_URL
+
 # Application definition
 
 INSTALLED_APPS = (

pythonie/pythonie/settings/dev.py

@@ -10,6 +10,9 @@
 
 EMAIL_BACKEND = "django.core.mail.backends.console.EmailBackend"
 
+# Override Wagtail admin base URL for local development
+WAGTAILADMIN_BASE_URL = "http://localhost:8000"
+
 # SQLite (simplest install)
 DATABASES = {
     "default": {

pythonie/pythonie/settings/tests.py

@@ -10,6 +10,9 @@
 
 EMAIL_BACKEND = "django.core.mail.backends.console.EmailBackend"
 
+# Override Wagtail admin base URL for tests
+WAGTAILADMIN_BASE_URL = "http://testserver"
+
 # SQLite (simplest install)
 DATABASES = {
     "default": {