feat: DB-agent feature sync with conflict detection

- ConsoleFeature 增加 Available/Conflict 字段
- pageConsole 显示 agent 全部能力（含不可用的），不可用项 disabled
- DB 已启用但 agent 不可用时标记为冲突 ⚠
- 不可用功能 hover 显示原因

internal/web/ui.go

@@ -933,9 +933,10 @@ func (u *UI) pageConsole(w http.ResponseWriter, r *http.Request) {
             }
             features := make([]ConsoleFeature, 0, len(capsResp.Capabilities))
             for _, c := range capsResp.Capabilities {
-                if c.Available {
-                    features = append(features, ConsoleFeature{Key: c.Key, Label: c.Label, Description: c.Description, Enabled: false})
-                }
+                features = append(features, ConsoleFeature{
+                    Key: c.Key, Label: c.Label, Description: c.Description,
+                    Available: c.Available, Enabled: false,
+                })
             }
             deviceAvailableFeatures[dev.DeviceID] = features
         }
@@ -1038,19 +1039,36 @@ func (u *UI) pageConsole(w http.ResponseWriter, r *http.Request) {
             activeKeys = map[string]bool{}
         }
 
-        // Features from device capabilities (filtered by agent /v1/capabilities).
-        // Fall back to persisted keys if agent doesn't respond.
+        // Features from device capabilities (from agent /v1/capabilities).
+        // Overlay persisted DB state for checkmarks and conflict detection.
         available := deviceAvailableFeatures[dev.DeviceID]
         var features []ConsoleFeature
         if len(available) > 0 {
             for _, f := range available {
                 f.Enabled = activeKeys[f.Key]
+                // Conflict: user enabled a feature that the device no longer supports.
+                if f.Enabled && !f.Available {
+                    f.Conflict = true
+                }
                 features = append(features, f)
             }
-        } else {
-            // Old agent: use persisted keys to show at least what's configured.
+            // Show persisted features that the agent didn't report (e.g. new features
+            // added to registry but old agent doesn't know them).
+            seen := map[string]bool{}
+            for _, f := range features {
+                seen[f.Key] = true
+            }
             for key := range activeKeys {
-                features = append(features, ConsoleFeature{Key: key, Label: key, Enabled: true})
+                if !seen[key] {
+                    features = append(features, ConsoleFeature{
+                        Key: key, Label: key, Enabled: true, Available: false, Conflict: true,
+                    })
+                }
+            }
+        } else {
+            // Old agent: show persisted keys.
+            for key := range activeKeys {
+                features = append(features, ConsoleFeature{Key: key, Label: key, Enabled: true, Available: true})
             }
         }
 
@@ -4732,4 +4750,6 @@ type ConsoleFeature struct {
     Label       string
     Description string
     Enabled     bool
+    Available   bool // device actually supports this (from agent /v1/capabilities)
+    Conflict    bool // enabled in DB but unavailable on device
 }

internal/web/ui/templates/console.html

@@ -61,8 +61,10 @@
         <table class="console-feature-table">
           {{range $f := $cd.Features}}
           <tr>
-            <td class="console-feature-check"><input type="checkbox" name="device_{{$cd.Device.DeviceID}}_feature" value="{{$f.Key}}"{{if $f.Enabled}} checked{{end}}></td>
-            <td class="console-feature-label" title="{{$f.Description}}">{{$f.Label}}</td>
+            <td class="console-feature-check"><input type="checkbox" name="device_{{$cd.Device.DeviceID}}_feature" value="{{$f.Key}}"{{if $f.Enabled}} checked{{end}}{{if not $f.Available}} disabled{{end}}></td>
+            <td class="console-feature-label{{if $f.Conflict}} text-danger{{else if not $f.Available}} text-muted{{end}}" title="{{$f.Description}}{{if $f.Conflict}} (设备已不支持){{else if not $f.Available}} (设备不支持){{end}}">
+              {{$f.Label}}{{if $f.Conflict}} ⚠{{end}}
+            </td>
           </tr>
           {{end}}
         </table>