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>

tests/test_provider_routing_bugs.py

@@ -318,7 +318,7 @@ class TestOpenRouterAliasRestrictions:
             os.environ.pop("OPENAI_API_KEY", None)
             os.environ.pop("XAI_API_KEY", None)
             os.environ["OPENROUTER_API_KEY"] = "test-key"
-            os.environ["OPENROUTER_ALLOWED_MODELS"] = "o3-mini,anthropic/claude-3-opus,flash"
+            os.environ["OPENROUTER_ALLOWED_MODELS"] = "o3-mini,anthropic/claude-opus-4,flash"
 
             # Register OpenRouter provider
             from providers.openrouter import OpenRouterProvider
@@ -330,7 +330,7 @@ class TestOpenRouterAliasRestrictions:
 
             expected_models = {
                 "openai/o3-mini",  # from alias
-                "anthropic/claude-3-opus",  # full name
+                "anthropic/claude-opus-4",  # full name
                 "google/gemini-2.5-flash",  # from alias
             }