feat(mcp): kebab__bulk_search tool (fb-42)

Exposes bulk multi-query search via MCP `bulk_search` tool:
- Input: { queries: [SearchInput shapes...] }, capped at 100
- Output: bulk_search_response.v1 with per-query results + summary
- Sequential execution reuses App instance for cache amortization
- Per-query errors embed error.v1 JSON; never aborts bulk call

Updates tool count from 7 to 8 in lib.rs comment + tools_list test.

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

crates/kebab-mcp/tests/tools_list.rs

@@ -1,13 +1,13 @@
-//! Integration: `build_tools_vec` returns 7 tools with correct names and
+//! Integration: `build_tools_vec` returns 8 tools with correct names and
 //! inputSchema. Uses the extracted `pub fn build_tools_vec()` helper — no
 //! transport or RequestContext needed.
 
 use kebab_mcp::build_tools_vec;
 
 #[test]
-fn tools_list_returns_seven_tools() {
+fn tools_list_returns_eight_tools() {
     let tools = build_tools_vec();
-    assert_eq!(tools.len(), 7, "expected exactly 7 tools, got {}", tools.len());
+    assert_eq!(tools.len(), 8, "expected exactly 8 tools, got {}", tools.len());
 
     let names: Vec<&str> = tools.iter().map(|t| t.name.as_ref()).collect();
     assert!(names.contains(&"schema"), "missing 'schema' tool");
@@ -17,6 +17,7 @@ fn tools_list_returns_seven_tools() {
     assert!(names.contains(&"ingest_file"), "missing 'ingest_file' tool");
     assert!(names.contains(&"ingest_stdin"), "missing 'ingest_stdin' tool");
     assert!(names.contains(&"fetch"), "missing 'fetch' tool");
+    assert!(names.contains(&"bulk_search"), "missing 'bulk_search' tool");
 }
 
 #[test]