feat: implement web UI for provider and model configuration

- Added 'provider_configs' and 'model_configs' tables to database.
- Refactored ProviderManager to support thread-safe dynamic updates and database overrides.
- Implemented 'Models' tab in dashboard to manage model visibility, mapping, and pricing.
- Added provider configuration modal to 'Providers' tab.
- Integrated database overrides into chat completion logic (enabled state, mapping, and cost).

src/providers/openai.rs

@@ -20,7 +20,10 @@ pub struct OpenAIProvider {
 impl OpenAIProvider {
     pub fn new(config: &crate::config::OpenAIConfig, app_config: &AppConfig) -> Result<Self> {
         let api_key = app_config.get_api_key("openai")?;
-        
+        Self::new_with_key(config, app_config, api_key)
+    }
+
+    pub fn new_with_key(config: &crate::config::OpenAIConfig, app_config: &AppConfig, api_key: String) -> Result<Self> {
         Ok(Self {
             client: reqwest::Client::new(),
             _config: config.clone(),