Batch rename of 22 test files. 62 references renamed total.
The full test suite is now GREEN again, matching the pre-rename baseline
from Task 1.1. Pure mechanical rename. No behavior change.
Files affected: test_ai_cache_tracking, test_ai_client_cli,
test_ai_client_result, test_api_events, test_context_pruner,
test_deepseek_provider, test_gemini_cli_* (3 files), test_gui2_mcp,
test_headless_* (2 files), test_live_gui_integration_v2,
test_orchestration_logic, test_phase6_engine, test_rag_integration,
test_run_worker_lifecycle_abort, test_spawn_interception_v2,
test_symbol_parsing, test_tier4_interceptor, test_tiered_aggregation,
test_token_usage.
Note: spec estimated 24 files; actual is 22 (test_deprecation_warnings
no longer exists, and 1 fewer file than spec's list).
Refs: conductor/tracks/send_result_to_send_20260616/
