This PR introduces several improvements to the CLI's WebDAV server and core services, focusing on performance, reliability, and better error handling.

Changes:

• Authentication caching: Added in-memory caching for auth details in AuthService and AuthMiddleware, reducing redundant token lookups and SDK re-initialization on every WebDAV request.
• Cache key centralization: Moved cache key constants from UsageService to CacheService as public static members, promoting reuse and centralizing cache key management.
• WebDAV MKCOL improvements: When a folder already exists, the handler now silently succeeds (returns 201) instead of throwing MethodNotAllowed, aligning with idempotent MKCOL semantics expected by many WebDAV clients.
• WebDAV PUT conflict handling: Replaced NotFoundError with ConflictError when attempting to PUT a file whose name clashes with an existing folder. Also restructured the handler to check for existing items before beginning the upload, and gracefully handles deletion failures.
• DatabaseService safety: Added an isInitialized guard to prevent re-initializing an already-initialized database connection.
• Dockerfile updates: Switched base image from node:24-alpine to node:24-bookworm-slim and adjusted healthcheck parameters for more conservative intervals.
• Test improvements: Standardized test descriptions to a consistent "should ..." pattern, added caching coverage for AuthMiddleware, and ensured cache is cleared between tests.