feat: interactive provider/model management with CRUD support

- Fix radioSelect duplicate title bug (add \r after cursor up)
- Add \x1B[K to clear hint line residual content
- Show "<- currently active" indicator for current provider/model
- Add Custom new provider creation (name, URL, key)
- Add Custom model name creation
- Add Remove provider with user selection + confirmation
- Add Remove model with user selection + confirmation
- Add Skip option in both provider and model selection
- Restructure flow: Provider → URL/Key config → Model → Sync
- Remove redundant URL/key prompts from model selection stage
- Add empty model array guard for NaN prevention
- Add loop-back after remove operations (stay on selection page)
- Enhance ModelPicker TUI with custom provider/model stages

Co-Authored-By: DeepSeek <noreply@deepseek.com>

Author: jimgqyu