feat: add ty type checking support and fix type issues

- Add ty.toml configuration with Django project root
- Add py.typed marker for type checking
- Fix type issues across codebase:
  - Add type ignore comments for redis.exceptions imports
  - Fix django.db.models.functions imports in utils
  - Fix getattr usage in accounts/forms
  - Remove unnecessary type annotations in dashboard/forms
- Configure ty to exclude migrations and respect ignore files
- All ty checks now pass (29 diagnostics -> 0)

.zed/settings.json

@@ -0,0 +1,14 @@
+{
+  "auto_install_extensions": { "ty": true },
+  "languages": {
+    "Python": {
+      "language_servers": [
+        // Disable basedpyright and enable Ty, and otherwise
+        // use the default configuration.
+        "ty",
+        "!basedpyright",
+        "..."
+      ]
+    }
+  }
+}