feat: implement provider credit tracking and balance management

- Added 'credit_balance' and 'low_credit_threshold' to 'provider_configs' table.
- Updated dashboard backend to support reading and updating provider credits.
- Implemented real-time credit deduction from provider balances on successful requests.
- Added visual balance indicators and configuration modal to the 'Providers' dashboard tab.

src/dashboard/mod.rs

@@ -536,7 +536,7 @@ async fn handle_get_providers(State(state): State<DashboardState>) -> Json<ApiRe
     let pool = &state.app_state.db_pool;
     
     // Load all overrides from database
-    let db_configs_result = sqlx::query("SELECT id, enabled, base_url FROM provider_configs")
+    let db_configs_result = sqlx::query("SELECT id, enabled, base_url, credit_balance, low_credit_threshold FROM provider_configs")
         .fetch_all(pool)
         .await;
         
@@ -546,7 +546,9 @@ async fn handle_get_providers(State(state): State<DashboardState>) -> Json<ApiRe
             let id: String = row.get("id");
             let enabled: bool = row.get("enabled");
             let base_url: Option<String> = row.get("base_url");
-            db_configs.insert(id, (enabled, base_url));
+            let balance: f64 = row.get("credit_balance");
+            let threshold: f64 = row.get("low_credit_threshold");
+            db_configs.insert(id, (enabled, base_url, balance, threshold));
         }
     }
 
@@ -566,12 +568,17 @@ async fn handle_get_providers(State(state): State<DashboardState>) -> Json<ApiRe
             _ => (false, "".to_string(), "Unknown"),
         };
 
+        let mut balance = 0.0;
+        let mut threshold = 5.0;
+
         // Apply database overrides
-        if let Some((db_enabled, db_url)) = db_configs.get(id) {
+        if let Some((db_enabled, db_url, db_balance, db_threshold)) = db_configs.get(id) {
             enabled = *db_enabled;
             if let Some(url) = db_url {
                 base_url = url.clone();
             }
+            balance = *db_balance;
+            threshold = *db_threshold;
         }
 
         // Find models for this provider in registry
@@ -606,6 +613,8 @@ async fn handle_get_providers(State(state): State<DashboardState>) -> Json<ApiRe
             "status": status,
             "models": models,
             "base_url": base_url,
+            "credit_balance": balance,
+            "low_credit_threshold": threshold,
             "last_used": None::<String>,
         }));
     }
@@ -625,6 +634,8 @@ struct UpdateProviderRequest {
     enabled: bool,
     base_url: Option<String>,
     api_key: Option<String>,
+    credit_balance: Option<f64>,
+    low_credit_threshold: Option<f64>,
 }
 
 async fn handle_update_provider(
@@ -637,12 +648,14 @@ async fn handle_update_provider(
     // Update or insert into database
     let result = sqlx::query(
         r#"
-        INSERT INTO provider_configs (id, display_name, enabled, base_url, api_key)
-        VALUES (?, ?, ?, ?, ?)
+        INSERT INTO provider_configs (id, display_name, enabled, base_url, api_key, credit_balance, low_credit_threshold)
+        VALUES (?, ?, ?, ?, ?, ?, ?)
         ON CONFLICT(id) DO UPDATE SET
             enabled = excluded.enabled,
             base_url = excluded.base_url,
             api_key = COALESCE(excluded.api_key, provider_configs.api_key),
+            credit_balance = COALESCE(excluded.credit_balance, provider_configs.credit_balance),
+            low_credit_threshold = COALESCE(excluded.low_credit_threshold, provider_configs.low_credit_threshold),
             updated_at = CURRENT_TIMESTAMP
         "#
     )
@@ -651,6 +664,8 @@ async fn handle_update_provider(
     .bind(payload.enabled)
     .bind(&payload.base_url)
     .bind(&payload.api_key)
+    .bind(payload.credit_balance)
+    .bind(payload.low_credit_threshold)
     .execute(pool)
     .await;