feat(search): overhaul search output formatting (GIT-5)

Phase 1: Add source_entity_iid to search results via CASE subquery on
hydrate_results() for all 4 source types (issue, MR, discussion, note).
Phase 2: Fix visual alignment - compute indent from prefix visible width.
Phase 3: Show compact relative time on title line.
Phase 4: Add drill-down hint footer (lore issues <iid>).
Phase 5: Move labels to --explain mode, limit snippets to 2 terminal lines.
Phase 6: Use section_divider() for results header.

Also: promote strip_ansi/visible_width to public render utils, update
robot mode --fields minimal search preset with source_entity_iid.

src/app/handlers.rs

@@ -1469,7 +1469,7 @@ async fn handle_search(
     if robot_mode {
         print_search_results_json(&response, elapsed_ms, args.fields.as_deref());
     } else {
-        print_search_results(&response);
+        print_search_results(&response, explain);
     }
     Ok(())
 }