feat(tui): wire entity cache for near-instant detail view reopens (bd-3rjw)

- Add get_mut() and clear() methods to EntityCache<V>
- Add CachedIssuePayload / CachedMrPayload types to state
- Wire cache check in navigate_to for instant cache hits
- Populate cache on IssueDetailLoaded / MrDetailLoaded
- Update cache on DiscussionsLoaded
- Add 6 new entity_cache tests (get_mut, clear)

crates/lore-tui/src/view/timeline.rs

@@ -124,7 +124,16 @@ pub fn render_timeline(
     } else {
         let bp = classify_width(area.width);
         let time_col_width = timeline_time_width(bp);
-        render_event_list(frame, state, area.x, y, area.width, list_height, clock, time_col_width);
+        render_event_list(
+            frame,
+            state,
+            area.x,
+            y,
+            area.width,
+            list_height,
+            clock,
+            time_col_width,
+        );
     }
 
     // -- Hint bar --