feat: major project restructure - move Django to backend dir and fix critical imports

- Restructure project: moved Django backend to backend/ directory
- Add frontend/ directory for future Next.js application
- Add shared/ directory for common resources
- Fix critical Django import errors:
  - Add missing sys.path modification for apps directory
  - Fix undefined CATEGORY_CHOICES imports in rides module
  - Fix media migration undefined references
  - Remove unused imports and f-strings without placeholders
- Install missing django-environ dependency
- Django server now runs without ModuleNotFoundError
- Update .gitignore and README for new structure
- Add pnpm workspace configuration for monorepo setup

config/django/test_accounts.py

@@ -1,44 +0,0 @@
-"""
-Test Django settings for thrillwiki accounts app.
-"""
-
-# Use in-memory database for tests
-DATABASES = {
-    "default": {
-        "ENGINE": "django.contrib.gis.db.backends.postgis",
-        "NAME": "test_db",
-    }
-}
-
-# Use a faster password hasher for tests
-PASSWORD_HASHERS = [
-    "django.contrib.auth.hashers.MD5PasswordHasher",
-]
-
-# Disable whitenoise for tests
-WHITENOISE_AUTOREFRESH = True
-STATICFILES_STORAGE = "whitenoise.storage.CompressedManifestStaticFilesStorage"
-
-INSTALLED_APPS = [
-    "django.contrib.admin",
-    "django.contrib.auth",
-    "django.contrib.contenttypes",
-    "django.contrib.sessions",
-    "django.contrib.messages",
-    "django.contrib.staticfiles",
-    "django.contrib.sites",
-    "allauth",
-    "allauth.account",
-    "allauth.socialaccount",
-    "accounts",
-    "core",
-    "pghistory",
-    "pgtrigger",
-    "email_service",
-    "parks",
-    "rides",
-    "media.apps.MediaConfig",
-]
-
-GDAL_LIBRARY_PATH = "/opt/homebrew/lib/libgdal.dylib"
-GEOS_LIBRARY_PATH = "/opt/homebrew/lib/libgeos_c.dylib"