fix(clippy): resolve rust 1.96 lint errors blocking the release gate

cargo clippy --workspace -D warnings fails on three pre-existing spots
newly flagged by the current toolchain: unnecessary_sort_by in
context_report, question_mark in the provider fallback chain, and
unnecessary_map_or in the empty-state widget check. Apply the
mechanical fixes clippy suggests; no behavior change.

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

crates/tui/src/context_report.rs

@@ -635,7 +635,7 @@ pub fn format_context_report(report: &PromptSourceMap) -> String {
 
 pub fn format_context_summary(report: &PromptSourceMap) -> String {
     let mut entries = report.entries.clone();
-    entries.sort_by(|a, b| b.estimated_tokens.cmp(&a.estimated_tokens));
+    entries.sort_by_key(|entry| std::cmp::Reverse(entry.estimated_tokens));
     let top = entries
         .iter()
         .take(5)

crates/tui/src/tui/app.rs

@@ -5217,9 +5217,7 @@ impl App {
 
     pub fn advance_fallback(&mut self, reason: impl Into<String>) -> Option<ApiProvider> {
         let reason = reason.into();
-        let Some(chain) = self.provider_chain.as_mut() else {
-            return None;
-        };
+        let chain = self.provider_chain.as_mut()?;
         let Some(next_kind) = chain.advance() else {
             self.last_fallback_reason = Some(format!(
                 "Fallback chain exhausted after {} provider(s): {reason}",

crates/tui/src/tui/widgets/mod.rs

@@ -2122,7 +2122,7 @@ fn should_render_empty_state(app: &App) -> bool {
     let active_is_empty = app
         .active_cell
         .as_ref()
-        .map_or(true, crate::tui::active_cell::ActiveCell::is_empty);
+        .is_none_or(crate::tui::active_cell::ActiveCell::is_empty);
     app.history.is_empty()
         && active_is_empty
         && !app.is_loading