refactor(workflow-file): phase1 migrate workflow file deps with compatibility bridge

Implement phase 1 of the file module migration by moving workflow-facing file primitives to core.workflow.file while keeping core.file as a temporary compatibility layer.

What this commit changes
- Add core.workflow.file package (constants/enums/models/helpers/file_manager/tool_file_parser).
- Add protocol-based runtime binding in core.workflow.file.runtime and core.workflow.file.protocols.
- Add application adapter core.app.workflow.file_runtime and bind runtime in extensions.ext_storage.init_app.
- Bind runtime in tests via tests/conftest.py.
- Migrate workflow-only imports from core.file.* to core.workflow.file.* across workflow runtime/nodes/entry/encoder and workflow node factory.
- Update workflow unit tests to patch/import the new workflow file namespace.
- Remove workflow-external-imports ignore_imports entries related to core.file from .importlinter.

Compatibility guarantee for phase split
- Keep core.file import path available in this phase by replacing core/file/*.py with forwarding bridge modules that re-export core.workflow.file symbols.
- Preserve runtime behavior and isinstance(File) identity consistency while non-workflow modules are still on legacy import paths.

Notes
- This commit intentionally does not remove core.file. Full repository replacement and bridge removal are handled in phase 2.

api/core/file/__init__.py

@@ -1,7 +1,17 @@
-from .constants import FILE_MODEL_IDENTITY
-from .enums import ArrayFileAttribute, FileAttribute, FileBelongsTo, FileTransferMethod, FileType
-from .models import (
+"""Compatibility bridge for legacy ``core.file`` imports.
+
+Phase 1 keeps this package as a forwarding layer while canonical file models and
+helpers live under ``core.workflow.file``.
+"""
+
+from core.workflow.file import (
+    FILE_MODEL_IDENTITY,
+    ArrayFileAttribute,
     File,
+    FileAttribute,
+    FileBelongsTo,
+    FileTransferMethod,
+    FileType,
     FileUploadConfig,
     ImageConfig,
 )