[BUG] 500/405 error when adding Season to tracker: get_tv() bucket mismatch triggers duplicate key IntegrityError on app_tv_unique_item_user

[Aresitoo]

Bug Description

When attempting to add a season to the tracker (e.g. via the Season detail page / track modal), POST /media_save crashes with HTTP 500:

django.db.utils.IntegrityError: duplicate key value violates unique constraint "app_tv_unique_item_user"
DETAIL: Key (user_id, item_id)=(1, 12457) already exists.

Because the form submission fails with a 500 error, browser navigation falls back to GET /media_save, displaying a blank page with HTTP ERROR 405 (Method Not Allowed).

Root Cause

1. In app/models/tv.py -> Season.get_tv():

   is_anime_bucket = self.item.library_media_type == MediaTypes.ANIME.value
   
   def _bucket_scoped(queryset):
       if is_anime_bucket:
           return queryset.filter(item__library_media_type=MediaTypes.ANIME.value)
       return queryset.exclude(item__library_media_type=MediaTypes.ANIME.value)

2. If a show was originally created in the library under library_media_type="anime", but a new season is accessed/created via a route/metadata where library_media_type="tv" (or vice-versa), _bucket_scoped() raises TV.DoesNotExist because the existing TV row has the other bucket type.
3. In except TV.DoesNotExist:, get_tv() assumes no TV record exists for the user and tries to create a new TV(item=item, user=self.user).
4. However, Item.objects.get_or_create(...) finds the existing parent show Item, so saving the new TV instance attempts to insert a duplicate (user_id, item_id) pair, violating the UniqueConstraint on TV.

Additional Bug in Item.fetch_releases()

Item.fetch_releases() in app/models/item.py calls events.tasks.reload_calendar.apply_async(...), but events/__init__.py is empty and app/models/item.py only does import events, causing:
AttributeError: module 'events' has no attribute 'tasks'

Proposed Fix

1. In app/models/tv.py -> Season.get_tv():
   Add a fallback check before creating a new TV instance:

   except TV.DoesNotExist:
       existing_tv = (
           TV.objects.filter(
               item__media_id=self.item.media_id,
               item__media_type=MediaTypes.TV.value,
               item__season_number=None,
               item__source=self.item.source,
               user=self.user,
           )
           .order_by("id")
           .first()
       )
       if existing_tv is not None:
           return existing_tv

2. In events/__init__.py:
   Add from . import tasks so events.tasks is always available when importing events.

[dannyvfilms]

Fixed in c53da28 on latest: Season.get_tv() now scopes the Item.get_or_create fallback by library_media_type (matching the existing bucket-scoped TV lookup from #623), so it can no longer collide with the other bucket's TV row. Also fixed the events.tasks AttributeError via a lazy import in Item.fetch_releases(). (Auto-closed by the commit's "Fixes #997" line.)