bake: report the stylesheet path in posix form

The accept's `css.file` is a path the agent reads back, so it is
normalised like the wrap step's files; the stylesheet-search test compares
posix paths too. Both showed up on the Windows job as backslashes.

Written with AI assistance (Claude).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/live/src/bake.rs

@@ -533,12 +533,12 @@ mod tests {
         std::fs::write(dir.join("src/styles.css"), ".pricing-grid { display: grid }\n.pricing-card { padding: 1px }").unwrap();
         std::fs::write(dir.join("node_modules/x/x.css"), ".pricing-grid { color: red }").unwrap();
         let cwd = dir.to_string_lossy().into_owned();
-        let found = find_owning_stylesheet(&cwd, "div.pricing-grid").unwrap();
+        let found = jsp::to_posix(&find_owning_stylesheet(&cwd, "div.pricing-grid").unwrap());
         assert!(found.ends_with("src/styles.css"), "{found}");
         assert_eq!(find_owning_stylesheet(&cwd, "div.nothing-here"), None);
         std::fs::remove_file(dir.join("src/styles.css")).unwrap();
         // One stylesheet in the app: it is the one.
-        let only = find_owning_stylesheet(&cwd, "div.nothing-here").unwrap();
+        let only = jsp::to_posix(&find_owning_stylesheet(&cwd, "div.nothing-here").unwrap());
         assert!(only.ends_with("src/reset.css"), "{only}");
         let _ = std::fs::remove_dir_all(&dir);
     }

crates/live/src/live_accept.rs

@@ -489,7 +489,7 @@ fn accept_cli(args: &[String], io: &mut Io) -> i32 {
                         m.insert(
                             "css".into(),
                             json!({
-                                "file": css_file.as_deref().map(|f| jsp::relative("/", &cwd, f)),
+                                "file": css_file.as_deref().map(|f| jsp::to_posix(&jsp::relative("/", &cwd, f))),
                                 "rules": rules,
                                 "anchor": anchor,
                             }),