feat: Update Claude model references from v3 to v4 (fixes issue #118) (#119)

* feat: Update Claude model references from v3 to v4

- Update model configurations from claude-3-opus to claude-4-opus
- Update model configurations from claude-3-sonnet to claude-4-sonnet
- Maintain backward compatibility through existing aliases (opus, sonnet, claude)
- Update provider registry preferred models list
- Update all test cases and assertions to reflect new model names
- Update documentation and examples consistently across all files
- Add Claude 4 model support while preserving existing functionality

Files modified: 15 (config, docs, providers, tests, tools)
Pattern: Systematic claude-3-* → claude-4-* model reference migration

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

Co-Authored-By: Claude <noreply@anthropic.com>

* PR feedback: changed anthropic/claude-4-opus -> anthropic/claude-opus-4 and anthropic/claude-4-haiku -> anthropic/claude-3.5-haiku

* changed anthropic/claude-4-sonnet -> anthropic/claude-sonnet-4

* PR feedback removed specific model from test mock

* PR feedback removed base.py

---------

Co-authored-by: Omry Nachman <omry@wix.com>
Co-authored-by: Claude <noreply@anthropic.com>

docs/adding_providers.md

@@ -690,7 +690,7 @@ When a user requests a model (e.g., "pro", "o3", "example-large-v1"), the system
 2. OpenAI skips (Gemini already handled it)
 3. OpenRouter never sees it
 
-### Example: Model "claude-3-opus" 
+### Example: Model "claude-4-opus" 
 
 1. **Gemini provider** checks: NO, not my model → skip
 2. **OpenAI provider** checks: NO, not my model → skip