docs: 📚 update documentation for Claude Opus 4.5 support and fix gitignore

Add comprehensive documentation for the newly supported Claude Opus 4.5 model via Antigravity provider across README and DOCUMENTATION files.

- Document Claude Opus 4.5 as Anthropic's most powerful model now available through Antigravity
- Add technical details about `claude-opus-4-5-thinking` internal model name
- Highlight `thinkingBudget` parameter support and thinking preservation features
- Update feature lists to emphasize Claude Opus 4.5 availability alongside existing Gemini 3 and Sonnet 4.5
- Generalize Claude-specific notes from "Sonnet 4.5" to "Claude" models for broader applicability
- Fix `.gitignore` entry to correctly ignore `oauth_creds/` directory instead of file

.gitignore

@@ -129,4 +129,4 @@ logs/
 cache/
 *.env
 
-oauth_creds
+oauth_creds/

DOCUMENTATION.md

@@ -391,7 +391,7 @@ A modular, shared caching system for providers to persist conversation state acr
 
 ### 3.5. Antigravity (`antigravity_provider.py`)
 
-The most sophisticated provider implementation, supporting Google's internal Antigravity API for Gemini and Claude models.
+The most sophisticated provider implementation, supporting Google's internal Antigravity API for Gemini and Claude models (including **Claude Opus 4.5**, Anthropic's most powerful model).
 
 #### Architecture
 
@@ -418,6 +418,13 @@ The most sophisticated provider implementation, supporting Google's internal Ant
   - Automatic injection into functionCalls for multi-turn conversations
   - Fallback to bypass value if signature unavailable
 
+**Claude Opus 4.5 (NEW!):**
+- Anthropic's most powerful model, now available via Antigravity proxy
+- Uses internal model name `claude-opus-4-5-thinking` when reasoning is enabled
+- Uses `thinkingBudget` parameter for extended thinking control
+- Full support for tool use with schema cleaning
+- Same thinking preservation and sanitization features as Sonnet
+
 **Claude Sonnet 4.5:**
 - Proxied through Antigravity API (uses internal model name `claude-sonnet-4-5-thinking`)
 - Uses `thinkingBudget` parameter like Gemini 2.5

README.md

@@ -28,11 +28,13 @@ This project provides a powerful solution for developers building complex applic
 -   **OpenAI-Compatible Proxy**: Offers a familiar API interface with additional endpoints for model and provider discovery.
 -   **Advanced Model Filtering**: Supports both blacklists and whitelists to give you fine-grained control over which models are available through the proxy.
 
--   **🆕 Antigravity Provider**: Full support for Google's internal Antigravity API, providing access to Gemini 2.5, Gemini 3, and Claude Sonnet 4.5 models with advanced features:
+-   **🆕 Antigravity Provider**: Full support for Google's internal Antigravity API, providing access to Gemini 2.5, Gemini 3, and Claude models with advanced features:
+    - **🚀 NEW: Claude Opus 4.5** - Anthropic's most powerful model, now available via Antigravity!
+    - Claude Sonnet 4.5 with extended thinking support
     - Thought signature caching for multi-turn conversations
     - Tool hallucination prevention via parameter signature injection
     - Automatic thinking block sanitization for Claude models
-    - Note: Claude Sonnet 4.5 thinking mode requires careful conversation state management (see [Antigravity documentation](DOCUMENTATION.md#antigravity-claude-extended-thinking-sanitization) for details)
+    - Note: Claude thinking mode requires careful conversation state management (see [Antigravity documentation](DOCUMENTATION.md#antigravity-claude-extended-thinking-sanitization) for details)
 -   **🆕 Credential Prioritization**: Automatic tier detection and priority-based credential selection ensures paid-tier credentials are used for premium models that require them.
 -   **🆕 Weighted Random Rotation**: Configurable credential rotation strategy - choose between deterministic (perfect balance) or weighted random (unpredictable, harder to fingerprint) selection.
 -   **🆕 Enhanced Gemini CLI**: Improved project discovery, paid vs free tier detection, and Gemini 3 support with thoughtSignature caching.
@@ -504,12 +506,13 @@ The following advanced settings can be added to your `.env` file (or configured
     SKIP_OAUTH_INIT_CHECK=true
 
 
-#### **Antigravity (Advanced - Gemini 3 \Claude 4.5 Access)**
+#### **Antigravity (Advanced - Gemini 3 \ Claude Opus 4.5 / Sonnet 4.5 Access)**
 The newest and most sophisticated provider, offering access to cutting-edge models via Google's internal Antigravity API.
 
 **Supported Models:**
 -   Gemini 2.5 (Pro/Flash) with `thinkingBudget` parameter
 -   **Gemini 3 Pro (High/Low)** - Latest preview models
+-   **🆕 Claude Opus 4.5 + Thinking** - Anthropic's most powerful model via Antigravity proxy
 -   **Claude Sonnet 4.5 + Thinking** via Antigravity proxy
 
 **Advanced Features:**