refactor(workflow-file): phase2 replace remaining imports and remove core.file

Complete phase 2 of the file module migration by replacing the remaining repository-wide legacy imports and deleting the temporary core.file compatibility package introduced in phase 1.

What this commit changes
- Replace legacy core.file.* imports with core.workflow.file.* across:
  - controllers
  - core app/agent/datasource/prompt/rag/tools/variables
  - factories, fields, libs, models, services
  - otel parser integration points
  - unit and integration tests that referenced legacy paths
- Migrate residual runtime usages in app/task pipeline paths that still referenced core.file symbols.
- Update tests and model serialization helpers that relied on old module paths.
- Remove the compatibility bridge package entirely:
  - delete core/file/__init__.py
  - delete core/file/constants.py
  - delete core/file/enums.py
  - delete core/file/file_manager.py
  - delete core/file/helpers.py
  - delete core/file/models.py
  - delete core/file/tool_file_parser.py

Verification
- No Python references to core.file remain ( -> empty).
- Targeted regression tests for migrated file primitives and factory/type flows passed:
  - tests/unit_tests/core/test_file.py
  - tests/unit_tests/factories/test_variable_factory.py
  - tests/unit_tests/services/test_variable_truncator.py

Result
- The repository now uses core.workflow.file as the single canonical file namespace.
- The migration is fully split into two commits: phase 1 compatibility + phase 2 full cutover.

api/controllers/console/app/workflow_draft_variable.py

@@ -15,11 +15,11 @@ from controllers.console.app.error import (
 from controllers.console.app.wraps import get_app_model
 from controllers.console.wraps import account_initialization_required, edit_permission_required, setup_required
 from controllers.web.error import InvalidArgumentError, NotFoundError
-from core.file import helpers as file_helpers
 from core.variables.segment_group import SegmentGroup
 from core.variables.segments import ArrayFileSegment, FileSegment, Segment
 from core.variables.types import SegmentType
 from core.workflow.constants import CONVERSATION_VARIABLE_NODE_ID, SYSTEM_VARIABLE_NODE_ID
+from core.workflow.file import helpers as file_helpers
 from extensions.ext_database import db
 from factories.file_factory import build_from_mapping, build_from_mappings
 from factories.variable_factory import build_segment_with_type