Add startup cleanup service for soft-deleted tasks older than 30 days

[MessiasLima]

Description

Soft-deleted tasks accumulate locally (and remotely for premium subscribers) until they are permanently removed. This ticket adds a startup service that hard-deletes tasks whose soft-deletion is older than 30 days, respecting subscription status by only touching local data for free users.

Scope

• In scope: startup cleanup service, 30-day retention threshold, local database cleanup for all users, Supabase cleanup for subscribers, wiring to app launch.
• Out of scope: UI for retention settings, user-controlled deletion, sync conflict resolution.

Acceptance criteria

• GIVEN the app starts
  WHEN the cleanup service runs
  THEN it queries local tasks where isDeleted = true and lastUpdatedAt is older than 30 days
• GIVEN a soft-deleted local task is older than 30 days
  WHEN the cleanup service runs
  THEN the task is permanently deleted from the local database
• GIVEN the user is a premium subscriber
  WHEN the cleanup service runs
  THEN it also queries Supabase for soft-deleted tasks older than 30 days and hard-deletes them
• GIVEN the user is not subscribed
  WHEN the cleanup service runs
  THEN only the local database is checked and no remote calls are made
• GIVEN the cleanup service runs
  THEN soft-deleted tasks within the 30-day window are not deleted