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/workflow/file/helpers.py

@@ -0,0 +1,92 @@
+from __future__ import annotations
+
+import base64
+import hashlib
+import hmac
+import os
+import time
+import urllib.parse
+
+from .runtime import get_workflow_file_runtime
+
+
+def get_signed_file_url(upload_file_id: str, as_attachment: bool = False, for_external: bool = True) -> str:
+    runtime = get_workflow_file_runtime()
+    base_url = runtime.files_url if for_external else (runtime.internal_files_url or runtime.files_url)
+    url = f"{base_url}/files/{upload_file_id}/file-preview"
+
+    timestamp = str(int(time.time()))
+    nonce = os.urandom(16).hex()
+    key = runtime.secret_key.encode()
+    msg = f"file-preview|{upload_file_id}|{timestamp}|{nonce}"
+    sign = hmac.new(key, msg.encode(), hashlib.sha256).digest()
+    encoded_sign = base64.urlsafe_b64encode(sign).decode()
+    query: dict[str, str] = {"timestamp": timestamp, "nonce": nonce, "sign": encoded_sign}
+    if as_attachment:
+        query["as_attachment"] = "true"
+    query_string = urllib.parse.urlencode(query)
+
+    return f"{url}?{query_string}"
+
+
+def get_signed_file_url_for_plugin(filename: str, mimetype: str, tenant_id: str, user_id: str) -> str:
+    runtime = get_workflow_file_runtime()
+    # Plugin access should use internal URL for Docker network communication.
+    base_url = runtime.internal_files_url or runtime.files_url
+    url = f"{base_url}/files/upload/for-plugin"
+    timestamp = str(int(time.time()))
+    nonce = os.urandom(16).hex()
+    key = runtime.secret_key.encode()
+    msg = f"upload|{filename}|{mimetype}|{tenant_id}|{user_id}|{timestamp}|{nonce}"
+    sign = hmac.new(key, msg.encode(), hashlib.sha256).digest()
+    encoded_sign = base64.urlsafe_b64encode(sign).decode()
+    return f"{url}?timestamp={timestamp}&nonce={nonce}&sign={encoded_sign}&user_id={user_id}&tenant_id={tenant_id}"
+
+
+def get_signed_tool_file_url(tool_file_id: str, extension: str, for_external: bool = True) -> str:
+    runtime = get_workflow_file_runtime()
+    return runtime.sign_tool_file(tool_file_id=tool_file_id, extension=extension, for_external=for_external)
+
+
+def verify_plugin_file_signature(
+    *, filename: str, mimetype: str, tenant_id: str, user_id: str, timestamp: str, nonce: str, sign: str
+) -> bool:
+    runtime = get_workflow_file_runtime()
+    data_to_sign = f"upload|{filename}|{mimetype}|{tenant_id}|{user_id}|{timestamp}|{nonce}"
+    secret_key = runtime.secret_key.encode()
+    recalculated_sign = hmac.new(secret_key, data_to_sign.encode(), hashlib.sha256).digest()
+    recalculated_encoded_sign = base64.urlsafe_b64encode(recalculated_sign).decode()
+
+    if sign != recalculated_encoded_sign:
+        return False
+
+    current_time = int(time.time())
+    return current_time - int(timestamp) <= runtime.files_access_timeout
+
+
+def verify_image_signature(*, upload_file_id: str, timestamp: str, nonce: str, sign: str) -> bool:
+    runtime = get_workflow_file_runtime()
+    data_to_sign = f"image-preview|{upload_file_id}|{timestamp}|{nonce}"
+    secret_key = runtime.secret_key.encode()
+    recalculated_sign = hmac.new(secret_key, data_to_sign.encode(), hashlib.sha256).digest()
+    recalculated_encoded_sign = base64.urlsafe_b64encode(recalculated_sign).decode()
+
+    if sign != recalculated_encoded_sign:
+        return False
+
+    current_time = int(time.time())
+    return current_time - int(timestamp) <= runtime.files_access_timeout
+
+
+def verify_file_signature(*, upload_file_id: str, timestamp: str, nonce: str, sign: str) -> bool:
+    runtime = get_workflow_file_runtime()
+    data_to_sign = f"file-preview|{upload_file_id}|{timestamp}|{nonce}"
+    secret_key = runtime.secret_key.encode()
+    recalculated_sign = hmac.new(secret_key, data_to_sign.encode(), hashlib.sha256).digest()
+    recalculated_encoded_sign = base64.urlsafe_b64encode(recalculated_sign).decode()
+
+    if sign != recalculated_encoded_sign:
+        return False
+
+    current_time = int(time.time())
+    return current_time - int(timestamp) <= runtime.files_access_timeout