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/application/services/nextcloud_file_id_service.rs

@@ -0,0 +1,110 @@
+use std::sync::Arc;
+
+use crate::common::errors::{DomainError, ErrorKind, Result};
+use crate::infrastructure::repositories::pg::NextcloudObjectIdRepository;
+
+#[derive(Clone)]
+pub struct NextcloudFileIdService {
+    repo: Option<Arc<NextcloudObjectIdRepository>>,
+    instance_id: String,
+}
+
+impl NextcloudFileIdService {
+    pub fn new(repo: Arc<NextcloudObjectIdRepository>, instance_id: String) -> Self {
+        Self {
+            repo: Some(repo),
+            instance_id,
+        }
+    }
+
+    pub fn new_stub() -> Self {
+        Self {
+            repo: None,
+            instance_id: "ocnca".to_string(),
+        }
+    }
+
+    pub async fn get_or_create_file_id(&self, file_id: &str) -> Result<i64> {
+        let repo = self.repo.as_ref().ok_or_else(|| {
+            DomainError::internal_error("NextcloudFileId", "Repository not initialized")
+        })?;
+        repo.get_or_create("file", file_id).await
+    }
+
+    pub async fn get_or_create_folder_id(&self, folder_id: &str) -> Result<i64> {
+        let repo = self.repo.as_ref().ok_or_else(|| {
+            DomainError::internal_error("NextcloudFileId", "Repository not initialized")
+        })?;
+        repo.get_or_create("folder", folder_id).await
+    }
+
+    /// Get the OxiCloud file UUID from a Nextcloud numeric ID.
+    pub async fn get_oxicloud_id(&self, nc_file_id: i64) -> Result<String> {
+        let repo = self.repo.as_ref().ok_or_else(|| {
+            DomainError::internal_error("NextcloudFileId", "Repository not initialized")
+        })?;
+        repo.get_object_id(nc_file_id, "file").await
+    }
+
+    pub fn format_oc_id(&self, id: i64) -> String {
+        format!("{:08}{}", id, self.instance_id)
+    }
+
+    pub fn instance_id(&self) -> &str {
+        &self.instance_id
+    }
+
+    #[cfg(test)]
+    pub fn new_test(instance_id: &str) -> Self {
+        Self {
+            repo: None,
+            instance_id: instance_id.to_string(),
+        }
+    }
+
+    pub fn ensure_ready(&self) -> Result<()> {
+        if self.repo.is_none() {
+            return Err(DomainError::new(
+                ErrorKind::InternalError,
+                "NextcloudFileId",
+                "Repository not initialized",
+            ));
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_format_oc_id_default_instance() {
+        let svc = NextcloudFileIdService::new_stub();
+        assert_eq!(svc.format_oc_id(42), "00000042ocnca");
+    }
+
+    #[test]
+    fn test_format_oc_id_custom_instance() {
+        let svc = NextcloudFileIdService::new_test("myinst");
+        assert_eq!(svc.format_oc_id(1), "00000001myinst");
+    }
+
+    #[test]
+    fn test_format_oc_id_large_number() {
+        let svc = NextcloudFileIdService::new_stub();
+        assert_eq!(svc.format_oc_id(123456789), "123456789ocnca");
+    }
+
+    #[test]
+    fn test_instance_id() {
+        let svc = NextcloudFileIdService::new_stub();
+        assert_eq!(svc.instance_id(), "ocnca");
+    }
+
+    #[test]
+    fn test_ensure_ready_fails_on_stub() {
+        let svc = NextcloudFileIdService::new_stub();
+        assert!(svc.ensure_ready().is_err());
+    }
+}