fix: stabilize core error handling

Remove production panic and unwrap paths from core modules.

Propagate bookmark encryption failures, harden file watcher and temp mapped file handling, and clean up dead code in shared utilities.

src/explorer/builder.rs

@@ -24,7 +24,7 @@ impl FileExplorerBuilder {
 
     /// Take FileExplorer out of builder
     pub fn build(&mut self) -> FileExplorer {
-        self.explorer.take().unwrap()
+        self.explorer.take().unwrap_or_default()
     }
 
     /// Enable HIDDEN_FILES option