feat(core,fuse,gui): show a sync issue on its node in the file browser

A refused change was only on the Sync page. A folder listing now carries
each node's issue (by local id, so a file not yet on Drive has it too),
and the browser's badge ranks it first, folders included, with the
issue's explanation as its tooltip. The event sampler publishes Files
when the set of issues changes, so the badge comes and goes with it.

crates/pdfs-core/src/control.rs

@@ -1296,6 +1296,10 @@ pub struct DirEntry {
     /// not known, and for anything not in the trash.
     #[serde(default)]
     pub trashed_from: Option<String>,
+    /// Why Drive refused a change queued on the node, for a [`Request::ListDir`]
+    /// entry; `None` otherwise.
+    #[serde(default)]
+    pub issue: Option<SyncIssue>,
 }
 
 /// One hit in a [`Request::Search`] result. Like [`DirEntry`] but carries the