refactor(ai_client): remove unused history management and bleed stats helpers

tests/test_token_viz.py

@@ -47,13 +47,6 @@ def test_add_bleed_derived_headroom_clamped_to_zero() -> None:
  result = ai_client._add_bleed_derived(d)
  assert result["headroom"] == 0
 
-def test_get_history_bleed_stats_returns_all_keys_unknown_provider() -> None:
- """get_history_bleed_stats must return a valid dict even if provider is unknown."""
- ai_client.set_provider("unknown", "unknown")
- stats = ai_client.get_history_bleed_stats()
- for key in ["provider", "limit", "current", "percentage", "estimated_prompt_tokens", "headroom", "would_trim", "sys_tokens", "tool_tokens", "history_tokens"]:
-  assert key in stats
-
 def test_app_token_stats_initialized_empty(app_instance: Any) -> None:
  """App._token_stats should start empty."""
  assert app_instance.controller._token_stats == {}