refactor: invert hide_zero_spend → show_zero_spend, default False

Changes the API from opt-in hiding (hide_zero_spend) to opt-in showing
(show_zero_spend). Default behavior now hides sub-bash.001 models and
shows the summary line — cleaner for the common case where free-tier
models dominate the breakdown.

- Renamed parameter: hide_zero_spend → show_zero_spend
- Inverted logic: default False means hide by default
- Updated docstrings, README, ARCHITECTURE.md

ARCHITECTURE.md

@@ -93,7 +93,7 @@ Healthy: 8  |  Unhealthy: 0
 
 **LiteLLM Endpoint:** `GET {litellm_url}/user/daily/activity`
 **Auth:** `Authorization: Bearer {litellm_master_key}`
-**Params:** `start_date` (YYYY-MM-DD or natural language shortcut), `end_date` (YYYY-MM-DD or natural language shortcut), `hide_zero_spend` (bool, default False)
+**Params:** `start_date` (YYYY-MM-DD or natural language shortcut), `end_date` (YYYY-MM-DD or natural language shortcut), `show_zero_spend` (bool, default False)
 
 ### Natural Language Date Resolution
 
@@ -109,9 +109,11 @@ The `_resolve_date()` helper converts natural language shortcuts to YYYY-MM-DD b
 
 Already-formatted YYYY-MM-DD strings pass through unchanged. Unrecognized strings are passed to the API, which will reject them with a clear error.
 
-### hide_zero_spend Parameter
+### show_zero_spend Parameter
 
-When `hide_zero_spend=True`, models with sub-$0.001 spend are filtered from the per-model breakdown. This is useful when free-tier or subscription models (e.g., Ollama Cloud) dominate the report with high token counts but negligible cost. Hidden models are summarized as `... (N model(s) with sub-$0.001 spend hidden)`.
+When `show_zero_spend=False` (the default), models with sub-$0.001 spend are hidden from the per-model breakdown and summarized as `... (N model(s) with sub-$0.001 spend hidden)`. This is the recommended default because free-tier or subscription models (e.g., Ollama Cloud) often dominate the report with high token counts but negligible cost, drowning out the models that actually cost money.
+
+Set `show_zero_spend=True` to see all models, including those with zero or near-zero spend.
 
 ### Response Processing
 
@@ -256,7 +258,7 @@ These are documented but not in scope for v1. The two-function design is the rig
 
 ### v1.2.0 (2026-06-13)
 - **feat:** Natural language date shortcuts for `litellm_cost()` — `today`, `yesterday`, `monday`, `last week`, etc.
-- **feat:** `hide_zero_spend` parameter for `litellm_cost()` — filters sub-$0.001 models from breakdown
+- **feat:** `show_zero_spend` parameter for `litellm_cost()` — default False hides sub-$0.001 models with summary line
 - **fix:** Cost report header shows resolved YYYY-MM-DD dates instead of raw shortcuts
 
 ### v1.1.0 (2026-06-13)