feat: Add support for Claude Opus 4.5 model

- Add claude-opus-4-5-20250929 to CLAUDE_MODELS in constants.py
- Update README.md documentation with new Opus 4.5 model
- Position as most capable model in the 4.5 family

Resolves #26

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Richard A <RichardAtCT@users.noreply.github.com>

Author: claude[bot]

README.md

@@ -622,6 +622,7 @@ for chunk in stream:
 All Claude models through November 2025 are supported:
 
 ### Claude 4.5 Family (Latest - Fall 2025)
+- **`claude-opus-4-5-20250929`** 🎯 Most Capable - Latest Opus with enhanced reasoning and capabilities
 - **`claude-sonnet-4-5-20250929`** ⭐ Recommended - Best coding model, superior reasoning and math
 - **`claude-haiku-4-5-20251001`** ⚡ Fast & Cheap - Similar performance to Sonnet 4 at 1/3 cost
 

src/constants.py

@@ -47,6 +47,7 @@
 # NOTE: Claude Agent SDK only supports Claude 4+ models, not Claude 3.x
 CLAUDE_MODELS = [
     # Claude 4.5 Family (Latest - Fall 2025) - RECOMMENDED
+    "claude-opus-4-5-20250929",   # Latest Opus 4.5 - Most capable
     "claude-sonnet-4-5-20250929",  # Recommended - best coding model
     "claude-haiku-4-5-20251001",  # Fast & cheap
     # Claude 4.1