fix: log resolved model name instead of group name in Recent Activity

When using model groups (e.g. 'deepseek-auto'), the dashboard logged the
group name instead of the concrete resolved model (e.g. 'deepseek-reasoner').

Now:
- logRequest passes the resolved modelID (concrete) + modelGroup (group name)
- RequestLog struct has a new ModelGroup field (omitempty)
- Dashboard displays resolved model (via group) when a group was used

Files changed:
  internal/server/logging.go  - add ModelGroup field
  internal/server/server.go   - pass resolved modelID, capture modelGroup
  static/js/websocket.js      - show group annotation in Recent Activity
  static/js/pages/overview.js - show group annotation in overview table
  static/js/pages/monitoring.js - show group annotation in stream

static/js/pages/overview.js

@@ -252,7 +252,7 @@ class OverviewPage {
                     <td>${time}</td>
                     <td><span class="badge-client">${request.client_id}</span></td>
                     <td>${request.provider}</td>
-                    <td><code class="code-sm">${request.model}</code></td>
+                    <td><code class="code-sm">${request.model}${request.model_group ? ` (via ${request.model_group})` : ''}</code></td>
                     <td>${request.tokens.toLocaleString()}</td>
                     <td>
                         <span class="status-badge ${statusClass}">
@@ -313,7 +313,7 @@ class OverviewPage {
             <td>${time}</td>
             <td><span class="badge-client">${request.client_id}</span></td>
             <td>${request.provider}</td>
-            <td><code class="code-sm">${request.model}</code></td>
+            <td><code class="code-sm">${request.model}${request.model_group ? ` (via ${request.model_group})` : ''}</code></td>
             <td>${(request.total_tokens || request.tokens || 0).toLocaleString()}</td>
             <td>
                 <span class="status-badge ${statusClass}">