feat(nextcloud): add Nextcloud-compatible API layer

Implement a complete Nextcloud client compatibility layer so that
Nextcloud desktop/mobile sync clients can connect to OxiCloud.

Key additions:
- Login Flow v2 (device auth) with OIDC bridge support
- WebDAV handler compatible with Nextcloud clients (PROPFIND, GET,
  PUT, DELETE, MKCOL, MOVE, COPY, HEAD, PROPPATCH)
- OCS API endpoints (user info, capabilities, notifications stubs,
  sharees, unified search)
- Basic Auth middleware with app password verification, account
  lockout integration, and blake3-keyed auth cache
- App password management: create, list, revoke via both native
  API (JWT-authenticated profile page) and Nextcloud OCS endpoints
- Nextcloud file ID mapping (oc:fileid) with persistent DB storage
- Chunked upload support (Nextcloud v2 chunking protocol)
- Trashbin WebDAV interface
- Avatar (SVG placeholder) and preview (redirect) handlers
- User profile page with app password management UI
- URL user validation on all DAV routes (403 on mismatch)
- Database schema for app_passwords and nextcloud_object_ids tables

All services are behind a `nextcloud.enabled` config flag and
cleanly separated under src/interfaces/nextcloud/.

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

src/domain/repositories/user_repository.rs

@@ -69,6 +69,9 @@ pub trait UserRepository: Send + Sync + 'static {
     /// Lists users with pagination
     async fn list_users(&self, limit: i64, offset: i64) -> UserRepositoryResult<Vec<User>>;
 
+    /// Searches users by username or email (SQL ILIKE) with a limit.
+    async fn search_users(&self, query: &str, limit: i64) -> UserRepositoryResult<Vec<User>>;
+
     /// Activates or deactivates a user
     async fn set_user_active_status(&self, user_id: &str, active: bool)
     -> UserRepositoryResult<()>;