feat(nc-webdav): generic dead-props on PROPPATCH/PROPFIND/REPORT

NC PROPPATCH only special-cased oc:favorite, silently dropped every
other prop while claiming 200. PROPFIND had no dead-prop lookup at
all. Reuse native /webdav/ dead-prop plumbing (now pub(crate)) so NC
surface gets real RFC 4918 §4.2 storage. Missing resource on
PROPPATCH is now 404 instead of a fake success no-op.

src/interfaces/api/handlers/webdav_handler.rs

@@ -1092,7 +1092,11 @@ async fn resolve_or_legacy(
 /// the dead-prop lookup is broken; surfacing a 500 here would mask the
 /// resource entirely from sync clients. The legacy path-keyed lookup
 /// behaved the same way (`.unwrap_or_default()`); we preserve it.
-async fn file_dead_props(
+///
+/// `pub(crate)` — also reused by the NextCloud-compatible PROPFIND
+/// handler (`interfaces::nextcloud::webdav_handler`), which needs the
+/// same lenient fetch for its own response writers.
+pub(crate) async fn file_dead_props(
     state: &Arc<AppState>,
     file: &FileDto,
 ) -> Vec<(QualifiedName, Option<String>)> {
@@ -1107,8 +1111,9 @@ async fn file_dead_props(
 }
 
 /// Same shape as `file_dead_props` but for folder rows. Used by the
-/// streaming PROPFIND walker.
-async fn folder_dead_props(
+/// streaming PROPFIND walker (and, via `pub(crate)`, by the NextCloud
+/// handler's own streaming walker).
+pub(crate) async fn folder_dead_props(
     store: &DeadPropertyStore,
     folder: &FolderDto,
 ) -> Vec<(QualifiedName, Option<String>)> {
@@ -1124,7 +1129,7 @@ async fn folder_dead_props(
 /// File-leaf variant for the streaming walker (takes a `&DeadPropertyStore`
 /// rather than the full `&Arc<AppState>` so it can be called from inside
 /// the async-stream future without cloning state).
-async fn streamed_file_dead_props(
+pub(crate) async fn streamed_file_dead_props(
     store: &DeadPropertyStore,
     file: &FileDto,
 ) -> Vec<(QualifiedName, Option<String>)> {