feat: implement WebDAV protocol support with WsgiDAV + account management API

Add complete WebDAV support: management REST API (CRUD accounts at /api/v1/webdav/accounts)
and DAV protocol endpoint (/dav) using WsgiDAV + a2wsgi bridge for client access via
HTTP Basic Auth. Includes Redis+TTLCache auth caching and integration tests (24 cases).

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

sqlmodels/__init__.py

@@ -75,7 +75,9 @@ from .object import (
     ObjectBase,
     ObjectCopyRequest,
     ObjectDeleteRequest,
+    ObjectFileFinalize,
     ObjectMoveRequest,
+    ObjectMoveUpdate,
     ObjectPropertyDetailResponse,
     ObjectPropertyResponse,
     ObjectRenameRequest,
@@ -115,7 +117,10 @@ from .source_link import SourceLink
 from .storage_pack import StoragePack
 from .tag import Tag, TagType
 from .task import Task, TaskProps, TaskPropsBase, TaskStatus, TaskType, TaskSummary
-from .webdav import WebDAV
+from .webdav import (
+    WebDAV, WebDAVBase,
+    WebDAVCreateRequest, WebDAVUpdateRequest, WebDAVAccountResponse,
+)
 from .file_app import (
     FileApp, FileAppType, FileAppExtension, FileAppGroupLink, UserFileAppDefault,
     # DTO