refactor(handlers): extract QueryParams + IngestParams to reduce complexity

query_handler refactored:
- Extract QueryParams struct with validation
- Extract SearchMethod enum
- Extract build_search_response helper
- Extract apply_rbac_filter helper
- Extract execute_hybrid_search helper
- Complexity: 14 → 6

ingest_handler helpers:
- Extract IngestParams struct with validation
- Extract IngestParamsError with responses
- Extract IngestResponse builder

New tests (18 total):
- QueryParams validation (10 tests)
- IngestParams validation (8 tests)

Total tests: 688 (was 670)

crates/mem-cli/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod endpoints;
+pub mod handlers;
 pub mod http_server;
 pub mod ingest_worker;
 pub mod query_worker;