feat(wire): search_hit.v1 + citation.v1 require indexed_at + stale (fb-32)

Additive minor — schema_version unchanged. Existing v1 consumers
that ignore unknown fields stay compatible; consumers that validate
strictly will reject pre-fb-32 payloads, which matches the wire
contract escape hatch (recipient version >= producer required).

Cross-task placeholders: kebab-eval / kebab-tui synthetic test
fixtures pin UNIX_EPOCH + stale=false (same pattern as
hybrid.rs / vector.rs). These don't exercise staleness — Task 11
adds dedicated TUI staleness rendering tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-tui/tests/search.rs

@@ -51,6 +51,10 @@ fn make_hit(rank: u32, path: &str, snippet: &str, citation: Citation) -> SearchH
         index_version: IndexVersion("v1".into()),
         embedding_model: Some(EmbeddingModelId("multilingual-e5-small".into())),
         chunker_version: ChunkerVersion("md-heading-v1".into()),
+        // fb-32: TUI search test fixtures pinned to UNIX_EPOCH + stale=false;
+        // staleness rendering covered in dedicated tests (Task 11).
+        indexed_at: time::OffsetDateTime::UNIX_EPOCH,
+        stale: false,
     }
 }