Summary

This updates WebDAV PUT replacement behavior to use Drive file replacement when an existing file is overwritten.

When a client uploads to an existing file path, the handler now uploads the new payload and calls the Drive replace endpoint. If replacement fails, it falls back to the previous delete-and-create behavior.

Why

WebDAV clients commonly create placeholder files and then immediately overwrite them with real content. Deleting the existing file before creating the replacement adds extra metadata operations and can slow down backup-style workloads.

Using replace-first behavior reduces that overhead while preserving the existing fallback path.

Behavior

• Existing file + non-empty upload: use Drive replaceFile.
• Replace failure: fall back to delete/create.
• Existing file + zero-byte upload: keep delete/create behavior.
• Existing folder at destination: still returns conflict.
• Response codes remain unchanged: 201 for create, 204 for replace.

Tests

• Added/updated PUT handler coverage for replace-first behavior.
• Verified targeted auth/WebDAV tests locally.