feat(webdav): add RFC 4331 quota-available-bytes/quota-used-bytes properties

Threads the caller's account-wide (used, available) storage figures through
PROPFIND for the plain-file WebDAV surface, resolved once per request via
StorageUsagePort::get_user_storage_info and reused for every folder entry
in the response. Unlimited accounts (quota <= 0) omit quota-available-bytes
entirely per RFC 4331 §3, rather than disclosing a sentinel value.
Properties are only advertised as known when the quota subsystem is enabled
and the lookup succeeds; otherwise they fall through to the standard 404
propstat.

src/interfaces/api/handlers/webdav_handler.rs

@@ -346,6 +346,33 @@ async fn resolve_webdav_scope_or_405(
     }
 }
 
+/// Resolve `(used_bytes, available_bytes)` for RFC 4331 quota properties.
+///
+/// `None` when the quota subsystem is disabled (`storage_usage_service` is
+/// only wired up behind its feature flag) or the lookup fails — callers
+/// treat that as "quota properties aren't known", not an error, since
+/// PROPFIND must still succeed for the rest of the response. Quota is
+/// account-wide, not per-folder, so this is resolved once per PROPFIND
+/// request and reused for every folder entry in the response.
+///
+/// `available_bytes` is itself `None` for unlimited accounts (quota <= 0):
+/// RFC 4331 §3 says a server MAY omit `quota-available-bytes` when there's
+/// no enforced/finite quota rather than disclose a made-up value, so
+/// callers drop the property (404 propstat) instead of reporting a
+/// sentinel like `i64::MAX`. `quota-used-bytes` is unaffected — it's a real
+/// measured value regardless of whether a limit exists.
+async fn resolve_quota(state: &Arc<AppState>, user_id: Uuid) -> Option<(i64, Option<i64>)> {
+    let storage_svc = state.storage_usage_service.as_ref()?;
+    let (used, quota_bytes) = storage_svc.get_user_storage_info(user_id).await.ok()?;
+    // Quota <= 0 means unlimited (see `StorageUsageService::check_storage_quota`).
+    let available = if quota_bytes <= 0 {
+        None
+    } else {
+        Some((quota_bytes - used).max(0))
+    };
+    Some((used, available))
+}
+
 fn join_drive_path(root_name: &str, subpath: &str) -> String {
     let subpath = subpath.trim_start_matches('/').trim_end_matches('/');
     if subpath.is_empty() {
@@ -557,6 +584,7 @@ async fn handle_propfind(
                 created_by: None,
                 updated_by: None,
             };
+            let quota = resolve_quota(&state, user.id).await;
             return build_streaming_propfind_response(
                 root_folder,
                 None, // folder_id = None → root children (drive-root folders)
@@ -567,6 +595,7 @@ async fn handle_propfind(
                 file_retrieval_service,
                 user.id,
                 state.webdav_dead_props.clone(),
+                quota,
             )
             .await;
         }
@@ -595,6 +624,7 @@ async fn handle_propfind(
                     )
                     .await?;
                 let folder_id = folder.id.clone();
+                let quota = resolve_quota(&state, user.id).await;
                 return build_streaming_propfind_response(
                     folder,
                     Some(folder_id),
@@ -605,6 +635,7 @@ async fn handle_propfind(
                     file_retrieval_service,
                     user.id,
                     state.webdav_dead_props.clone(),
+                    quota,
                 )
                 .await;
             }
@@ -659,6 +690,7 @@ async fn handle_propfind(
                 )
                 .await?;
             let folder_id = folder.id.clone();
+            let quota = resolve_quota(&state, user.id).await;
             return build_streaming_propfind_response(
                 folder,
                 Some(folder_id),
@@ -669,6 +701,7 @@ async fn handle_propfind(
                 file_retrieval_service,
                 user.id,
                 state.webdav_dead_props.clone(),
+                quota,
             )
             .await;
         }
@@ -732,6 +765,7 @@ async fn build_streaming_propfind_response(
     file_retrieval_service: std::sync::Arc<FileRetrievalService>,
     user_id: Uuid,
     dead_props_store: Arc<DeadPropertyStore>,
+    quota: Option<(i64, Option<i64>)>,
 ) -> Result<Response<Body>, AppError> {
     let depth = depth.to_string();
     let base_href = base_href.to_string();
@@ -752,7 +786,7 @@ async fn build_streaming_propfind_response(
             let mut w = Writer::new(&mut buf);
             WebDavAdapter::write_multistatus_start(&mut w)
                 .map_err(|e| std::io::Error::other(e.to_string()))?;
-            WebDavAdapter::write_folder_entry_with_dead_props(&mut w, &folder, &propfind_request, &base_href, &folder_dead)
+            WebDavAdapter::write_folder_entry_with_dead_props(&mut w, &folder, &propfind_request, &base_href, &folder_dead, quota)
                 .map_err(|e| std::io::Error::other(e.to_string()))?;
         }
         yield Bytes::from(buf);
@@ -795,7 +829,7 @@ async fn build_streaming_propfind_response(
                     let mut w = Writer::new(&mut chunk);
                     for (subfolder, child_dead) in result.items.iter().zip(subfolder_deads.iter()) {
                         let href = format!("{}{}/", base_href, encode_path_segment(&subfolder.name));
-                        WebDavAdapter::write_folder_entry_with_dead_props(&mut w, subfolder, &propfind_request, &href, child_dead)
+                        WebDavAdapter::write_folder_entry_with_dead_props(&mut w, subfolder, &propfind_request, &href, child_dead, quota)
                             .map_err(|e| std::io::Error::other(e.to_string()))?;
                     }
                 }