feat(m4b): add vault selection UI, enable/disable toggle, missing-installed UI

- Add VaultSelection.svelte: first-run vault create/open/recent UI
- Update App.svelte: vault check on startup, show VaultSelection when needed
- Update PluginCard.svelte: enable/disable buttons, vault state awareness
- Update PluginManager.svelte: enable/disable handlers, missing-installed section
- Add SetCurrentVault Wails API binding
- Add RecordDesiredPlugin Wails API binding
- Record desired plugins on discovery (only when vault open)
- Fix addRecent: remove duplicate sort, clean up unused import
- Update smoke-platform.sh: enable/disable lifecycle test
- Add runEnableDisableTest: vault create/open, disable/enable, plugins.json verify

internal/core/appsettings/manager.go

@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"sort"
 	"sync"
 	"time"
 )
@@ -237,19 +236,11 @@ func addRecent(list []string, path string, max int) []string {
 			filtered = append(filtered, p)
 		}
 	}
-	// Prepend
+	// Prepend (most recent first)
 	result := append([]string{path}, filtered...)
 	// Trim
 	if len(result) > max {
 		result = result[:max]
 	}
-	sort.SliceStable(result, func(i, j int) bool {
-		return result[i] < result[j]
-	})
-	// Actually keep insertion order: prepend is correct, just trim
-	result = append([]string{path}, filtered...)
-	if len(result) > max {
-		result = result[:max]
-	}
 	return result
 }