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/interfaces/nextcloud/status_handler.rs

@@ -0,0 +1,22 @@
+use axum::Json;
+use axum::extract::State;
+use axum::response::{IntoResponse, Response};
+use serde_json::json;
+use std::sync::Arc;
+
+use crate::common::di::AppState;
+
+pub async fn handle_status(State(state): State<Arc<AppState>>) -> Response {
+    let (major, minor, patch) = state.core.config.nextcloud.emulated_version;
+    let version_string = state.core.config.nextcloud.version_string();
+    Json(json!({
+        "installed": true,
+        "maintenance": false,
+        "needsDbUpgrade": false,
+        "version": format!("{}.{}.{}.1", major, minor, patch),
+        "versionstring": version_string,
+        "productname": "OxiCloud",
+        "edition": ""
+    }))
+    .into_response()
+}