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/database/mod.rs

@@ -78,6 +78,41 @@ async fn run_migrations(pool: &DbPool) -> Result<()> {
     .execute(pool)
     .await?;
 
+    // Create provider_configs table
+    sqlx::query(
+        r#"
+        CREATE TABLE IF NOT EXISTS provider_configs (
+            id TEXT PRIMARY KEY,
+            display_name TEXT NOT NULL,
+            enabled BOOLEAN DEFAULT TRUE,
+            base_url TEXT,
+            api_key TEXT,
+            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
+        )
+        "#
+    )
+    .execute(pool)
+    .await?;
+
+    // Create model_configs table
+    sqlx::query(
+        r#"
+        CREATE TABLE IF NOT EXISTS model_configs (
+            id TEXT PRIMARY KEY,
+            provider_id TEXT NOT NULL,
+            display_name TEXT,
+            enabled BOOLEAN DEFAULT TRUE,
+            prompt_cost_per_m REAL,
+            completion_cost_per_m REAL,
+            mapping TEXT,
+            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+            FOREIGN KEY (provider_id) REFERENCES provider_configs(id) ON DELETE CASCADE
+        )
+        "#
+    )
+    .execute(pool)
+    .await?;
+
     // Create indices
     sqlx::query(
         "CREATE INDEX IF NOT EXISTS idx_clients_client_id ON clients(client_id)"