Suffix the drop-indicator stroke width to avoid the f32 fallback

egui's Stroke::new takes `width: impl Into<f32>`, so the unsuffixed 2.0
literal had no concrete type to infer from and relied on rustc falling
back to f32. That fallback is being removed (rust#154024), and the
float_literal_f32_fallback lint already warns it will become a hard
error, so spell the type out as 2.0_f32.

No behaviour change - the literal was already compiling as f32. The only
other Stroke::new call site passes an f32 variable and was unaffected.
cargo build is now warning-free; clippy is down to the four long-standing
warnings in odt.rs and order.rs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GBWj9TphFMCoh7VHaSRnvQ

src/app/file_list.rs

@@ -84,8 +84,12 @@ impl App {
                                 ui.painter().hline(
                                     rect.x_range(),
                                     y,
+                                    // `Stroke::new` takes `impl Into<f32>`, which
+                                    // gives an unsuffixed literal no concrete type
+                                    // to infer; suffix it rather than lean on the
+                                    // f32 fallback that rustc is removing.
                                     egui::Stroke::new(
-                                        2.0,
+                                        2.0_f32,
                                         ui.visuals().selection.stroke.color,
                                     ),
                                 );