fix: register anthropic provider, normalize togetherAI alias, fix dsk_deepseek exception handling

- Add 'anthropic' to available_providers and unsafe_providers so users can set
  provider_name = anthropic in config.ini and use ANTHROPIC_API_KEY
- Add provider name alias normalization so 'togetherAI' (as documented in README)
  is accepted as equivalent to 'together'
- Fix NameError in dsk_deepseek: add 'as e' to AuthenticationError, RateLimitError,
  and NetworkError except clauses where 'e' was referenced but not bound
- Remove unreachable 'return thought' dead code at end of lm_studio_fn
- Update README to list Anthropic as a supported API provider

README.md

@@ -240,6 +240,7 @@ provider_server_address = # Typically ignored or can be left blank when is_local
 | Hugging Face | `huggingface`   | No     | Use models from Hugging Face Inference API.       | [huggingface.co/settings/tokens](https://huggingface.co/settings/tokens) |
 | TogetherAI   | `togetherAI`    | No     | Use various open-source models via TogetherAI API.| [api.together.ai/settings/api-keys](https://api.together.ai/settings/api-keys) |
 | OpenRouter   | `openrouter`    | No     | Use OpenRouter Models| [https://openrouter.ai/](https://openrouter.ai/) |
+| Anthropic    | `anthropic`     | No     | Use Claude models via Anthropic's API.            | [console.anthropic.com](https://console.anthropic.com/) |
 | MiniMax      | `minimax`       | No     | Use MiniMax M2.5 series models (e.g., MiniMax-M2.5).| [platform.minimax.io](https://platform.minimax.io/user-center/basic-information) |
 
 *Note:*