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).

static/js/dashboard.js

@@ -137,6 +137,7 @@ class Dashboard {
             case 'overview': return this.getOverviewTemplate();
             case 'clients': return this.getClientsTemplate();
             case 'providers': return this.getProvidersTemplate();
+            case 'models': return this.getModelsTemplate();
             case 'logs': return this.getLogsTemplate();
             case 'monitoring': return this.getMonitoringTemplate();
             case 'settings': return '<div class="loading-placeholder">Loading settings...</div>';
@@ -253,6 +254,30 @@ class Dashboard {
         `;
     }
 
+    getModelsTemplate() {
+        return `
+            <div class="card">
+                <div class="card-header">
+                    <div>
+                        <h3 class="card-title">Model Registry</h3>
+                        <p class="card-subtitle">Manage model availability and custom pricing</p>
+                    </div>
+                    <div class="card-actions">
+                        <input type="text" id="model-search" placeholder="Search models..." class="form-control" style="margin-bottom: 0; padding: 4px 8px; width: 250px;">
+                    </div>
+                </div>
+                <div class="table-container">
+                    <table class="table" id="models-table">
+                        <thead>
+                            <tr><th>ID</th><th>Display Name</th><th>Provider</th><th>Pricing (In/Out)</th><th>Context</th><th>Status</th><th>Actions</th></tr>
+                        </thead>
+                        <tbody></tbody>
+                    </table>
+                </div>
+            </div>
+        `;
+    }
+
     getLogsTemplate() {
         return `
             <div class="card">