refactor(gemini): 🔨 switch to sequential rotation mode and adjust tier priority for gemini-3 models

- Changed default rotation mode from "balanced" to "sequential" to optimize credential usage by sticking with one credential until rate-limited (429), then switching
- Updated Gemini-3 model tier requirement from priority 1 to priority 2 to correctly reflect paid tier credentials

src/rotator_library/providers/gemini_cli_provider.py

@@ -187,8 +187,8 @@ def _env_int(key: str, default: int) -> int:
 class GeminiCliProvider(GeminiAuthBase, ProviderInterface):
     skip_cost_calculation = True
 
-    # Balanced by default - Gemini CLI has short cooldowns (seconds, not hours)
-    default_rotation_mode: str = "balanced"
+    # Sequential mode - stick with one credential until it gets a 429, then switch
+    default_rotation_mode: str = "sequential"
 
     # =========================================================================
     # TIER CONFIGURATION
@@ -506,7 +506,7 @@ class GeminiCliProvider(GeminiAuthBase, ProviderInterface):
 
         # Gemini 3 requires paid tier
         if model_name.startswith("gemini-3-"):
-            return 1  # Only priority 1 (paid) credentials
+            return 2  # Only priority 2 (paid) credentials
 
         return None  # All other models have no restrictions