feat: implement HTMX support, DRF filters, and professionalized documentation

- Implement server-side location chaining with HTMX support via `htmx=True` in fields and widgets.
- Update location views to handle HTMX requests and return HTML <option> fragments.
- Add NepaliDateYearFilter and NepaliDateRangeFilter for robust DRF API filtering.
- Expand default `DATE_INPUT_FORMATS` in configuration to support multiple common Nepali date styles.
- Update DRF serializers to automatically respect global `NEPKIT` configuration settings.
- Add `django-filter` as an optional dependency under the `drf` extra in pyproject.toml.
- Correct underlying dependency references from `nepali-datetime` to nepali library.
- Complete overhaul of README.md for premium DX, including new sections for storage behavior, timezone awareness, and API usage.

example/demo/admin.py

@@ -10,14 +10,14 @@ class PersonAdmin(NepaliModelAdmin):
     list_display = (
         "name",
         "birth_date",
-        "birth_date_en",
+        "birth_date_ne",
         "phone_number",
         "province",
-        "province_en",
+        "province_ne",
         "district",
-        "district_en",
+        "district_ne",
         "municipality",
-        "municipality_en",
+        "municipality_ne",
         "created_at",
         "updated_at",
     )