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/action/trace.rs

@@ -40,13 +40,15 @@ pub fn fetch_trace(
 pub fn fetch_known_paths(conn: &Connection, project_id: Option<i64>) -> Result<Vec<String>> {
     let paths = if let Some(pid) = project_id {
         let mut stmt = conn.prepare(
-            "SELECT DISTINCT new_path FROM mr_file_changes WHERE project_id = ?1 ORDER BY new_path",
+            "SELECT DISTINCT new_path FROM mr_file_changes \
+             WHERE project_id = ?1 ORDER BY new_path LIMIT 5000",
         )?;
         let rows = stmt.query_map([pid], |row| row.get::<_, String>(0))?;
         rows.collect::<std::result::Result<Vec<_>, _>>()?
     } else {
-        let mut stmt =
-            conn.prepare("SELECT DISTINCT new_path FROM mr_file_changes ORDER BY new_path")?;
+        let mut stmt = conn.prepare(
+            "SELECT DISTINCT new_path FROM mr_file_changes ORDER BY new_path LIMIT 5000",
+        )?;
         let rows = stmt.query_map([], |row| row.get::<_, String>(0))?;
         rows.collect::<std::result::Result<Vec<_>, _>>()?
     };