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

litellm_dashboard.py

@@ -190,13 +190,13 @@ class Tools:
         self,
         start_date: str,
         end_date: str,
-        hide_zero_spend: bool = False,
+        show_zero_spend: bool = False,
     ) -> str:
         """
         Get LiteLLM cost breakdown for a date range.
         :param start_date: Start date — YYYY-MM-DD or natural language shortcut (e.g. "2026-06-01", "today", "yesterday", "monday", "last monday", "two days ago", "this week", "last month")
         :param end_date: End date — YYYY-MM-DD or natural language shortcut
-        :param hide_zero_spend: Hide models with sub-$0.001 spend (default False). Useful when free-tier or subscription models (e.g. Ollama Cloud) dominate the breakdown with high token counts but negligible cost.
+        :param show_zero_spend: Show models with sub-$0.001 spend (default False). When False, these models are hidden and summarized as "... (N model(s) with sub-$0.001 spend hidden)". Useful when free-tier or subscription models (e.g. Ollama Cloud) dominate the breakdown with high token counts but negligible cost.
         Returns formatted cost report with per-model and per-day breakdowns, token counts, cache hit rate, and request stats.
         """
         if not self.valves.litellm_master_key:
@@ -284,7 +284,7 @@ class Tools:
         hidden_count = 0
         for model_name in sorted(model_totals, key=lambda k: model_totals[k]["spend"], reverse=True):
             mt = model_totals[model_name]
-            if hide_zero_spend and mt["spend"] < 0.001:
+            if not show_zero_spend and mt["spend"] < 0.001:
                 hidden_count += 1
                 continue
             # Strip common provider prefixes for readability