feat(tasks): extend and harden the task system redesign

- TaskType: add EMPTY_TRASH, CHECK_WORKFLOWS, CLEANUP_SHARE_LINKS;
  remove INDEX_REBUILD (no backing task — beat schedule uses index_optimize)
- TRACKED_TASKS: wire up all nine task types including the three new ones
  and llmindex_index / process_mail_accounts
- Add task_revoked_handler so cancelled/expired tasks are marked REVOKED
- Fix double-write: task_postrun_handler no longer overwrites result_data
  when status is already FAILURE (task_failure_handler owns that write)
- v9 serialiser: map EMAIL_CONSUME and FOLDER_CONSUME to AUTO_TASK
- views: scope task list to owner for regular users, admins see all;
  validate ?days= query param and return 400 on bad input
- tests: add test_list_admin_sees_all_tasks; rename/fix
  test_parses_duplicate_string (duplicates produce SUCCESS, not FAILURE);
  use PaperlessTaskFactory in modified tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/documents/models.py

@@ -683,9 +683,11 @@ class PaperlessTask(ModelWithOwner):
         TRAIN_CLASSIFIER = "train_classifier", _("Train Classifier")
         SANITY_CHECK = "sanity_check", _("Sanity Check")
         INDEX_OPTIMIZE = "index_optimize", _("Index Optimize")
-        INDEX_REBUILD = "index_rebuild", _("Index Rebuild")
         MAIL_FETCH = "mail_fetch", _("Mail Fetch")
         LLM_INDEX = "llm_index", _("LLM Index")
+        EMPTY_TRASH = "empty_trash", _("Empty Trash")
+        CHECK_WORKFLOWS = "check_workflows", _("Check Workflows")
+        CLEANUP_SHARE_LINKS = "cleanup_share_links", _("Cleanup Share Links")
 
     COMPLETE_STATUSES = (
         Status.SUCCESS,