fix: warnings and icon rendering

- Remove unused imports (HashMap, TextEdit)
- Remove unnecessary mut on fonts
- Replace ✕ (U+2715) with × (U+00D7) for close/cross icons
- Replace ＋ (U+FF0B) with + (U+002B) for New Connection button
- Replace ▲/▼ (U+25B2/U+25BC) with ↑/↓ (U+2191/U+2193) for sort arrows

src/ui/panels/mod.rs

@@ -2,8 +2,7 @@ pub mod file_pane;
 pub mod local_pane;
 pub mod queue;
 pub mod remote_pane;
+pub mod sidebar;
 pub mod status_bar;
 pub mod tabs;
 pub mod toolbar;
-pub mod transfer_area;
-pub mod tree;