docs(fb-42): wire schema + README + SMOKE + design + SKILL + INDEX

- Add bulk_search_item.v1 + bulk_search_response.v1 wire schemas
- Register both in WIRE_SCHEMAS const
- README: --bulk flag mention + MCP tool list 7→8 (bulk_search)
- SMOKE: bulk multi-query walkthrough (CLI + MCP equivalent)
- Design §2.2: Bulk multi-query (fb-42) subsection (additive minor)
- SKILL: mcp__kebab__bulk_search section + tool table row
- Task spec status open→completed, banner replaced
- INDEX: fb-42 row 머지 (rerank hint deferred)
- Fix: missed Capabilities {bulk_search} in cli wire.rs test (Task 7 leftover)
- Fix: missed tools.len() 7→8 in cli_mcp_smoke (Task 5 leftover)

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

crates/kebab-cli/tests/cli_mcp_smoke.rs

@@ -66,8 +66,8 @@ fn cli_mcp_initialize_then_tools_list() {
         .expect("tools/list result.tools must be an array");
     assert_eq!(
         tools.len(),
-        7,
-        "expected 7 tools (schema, doctor, search, ask, fetch, ingest_file, ingest_stdin), got {}: {list}",
+        8,
+        "expected 8 tools (schema, doctor, search, bulk_search, ask, fetch, ingest_file, ingest_stdin), got {}: {list}",
         tools.len()
     );