docs: update README and ARCHITECTURE for show_failed parameter

- README: add show_failed to litellm_history params
- ARCHITECTURE: update params line and add Filtering section explaining
  show_failed=False behavior and header indicator

ARCHITECTURE.md

@@ -161,7 +161,7 @@ By Date:
 
 **LiteLLM Endpoint:** `GET {litellm_url}/spend/logs`
 **Auth:** `Authorization: Bearer {litellm_master_key}`
-**Params:** `limit` (int, 1-50, default 20), `show_cost` (bool, default true)
+**Params:** `limit` (int, 1-50, default 20), `show_cost` (bool, default true), `show_failed` (bool, default true)
 
 ### Response Processing
 
@@ -169,6 +169,8 @@ The `/spend/logs` endpoint returns **all** historical request logs (no server-si
 
 **Performance note:** For large deployments (thousands of logs), this endpoint can be slow. The tool caps `limit` at 50 and uses a 30s timeout.
 
+**Filtering:** When `show_failed=False`, requests with `metadata.exception` or `metadata.status="failure"` are filtered out before applying the `limit`. This hides auth probe noise, routing failures, and other non-essential errors. The header shows "(failed requests hidden)" when active.
+
 ### Per-Request Fields
 
 | Field | Description |