feat: plugin install/uninstall lifecycle + UI buttons

- AppConfig: add InstalledPlugins []string
- Manager.Discover(): no config dependency, all plugins start inactive
- Manager.SyncConfig(): apply installed/enabled state from AppConfig
- Manager.Enable(): works for plugins without on_install hook
- Manager.Install/Uninstall(): run on_install/on_uninstall hooks
- ActivatePlugin: skip if HasInstall && !Installed
- ReloadPlugins: Discover → SyncConfig → InitRuntimes
- Bindings: InstallPlugin, UninstallPlugin
- SettingsPlugins: install/uninstall buttons, toggle only after install
- Calendar: migration moved from on_init to on_install, on_uninstall drops tables
- Tests: all 12 pass (manager + runtime + calendar)

cmd/verstak-gui/bindings_plugins.go

@@ -18,6 +18,8 @@ type PluginDTO struct {
 	Author      string      `json:"author,omitempty"`
 	Description string      `json:"description,omitempty"`
 	Active      bool        `json:"active"`
+	Installed   bool        `json:"installed"`
+	HasInstall  bool        `json:"hasInstall"`
 	HasPanel    bool        `json:"hasPanel"`
 	HasSettings bool        `json:"hasSettings"`
 	UIContribs  UIContribDTO `json:"uiContribs"`
@@ -89,6 +91,8 @@ func (a *App) ListPlugins() []PluginDTO {
 			Author:      p.Meta.Author,
 			Description: p.Meta.Description,
 			Active:      active,
+			Installed:   p.Installed,
+			HasInstall:  p.HasInstall,
 			HasPanel:    hasPanel,
 			UIContribs:  contribs,
 		})
@@ -97,11 +101,22 @@ func (a *App) ListPlugins() []PluginDTO {
 }
 
 // SetPluginEnabled persists the enabled/disabled state and applies it to the runtime.
+// Returns error if the plugin is not installed but has install lifecycle.
 func (a *App) SetPluginEnabled(name string, enabled bool) error {
 	if a.plugins == nil {
 		return fmt.Errorf("plugin manager not ready")
 	}
 
+	if enabled {
+		if err := a.plugins.Enable(name); err != nil {
+			return err
+		}
+	} else {
+		if err := a.plugins.Disable(name); err != nil {
+			return err
+		}
+	}
+
 	appCfg, _ := config.LoadAppConfig()
 	if appCfg == nil {
 		appCfg = config.DefaultAppConfig()
@@ -207,26 +222,39 @@ func (a *App) ReloadPlugins() error {
 	log.Print("[plugins] reload requested")
 	a.plugins.CloseRuntimes()
 
-	appCfg, _ := config.LoadAppConfig()
-	if appCfg == nil {
-		appCfg = config.DefaultAppConfig()
-	}
-	enabledSet := make(map[string]bool)
-	for _, name := range appCfg.EnabledPlugins {
-		enabledSet[name] = true
-	}
 	a.plugins.Discover()
-	a.plugins.InitRuntimes()
+
+	appCfg, _ := config.LoadAppConfig()
+	a.plugins.SyncConfig(appCfg)
 
 	// Apply enable/disable state from config: deactivate everything not in enabled set
 	for _, p := range a.plugins.Plugins() {
-		if !enabledSet[p.Meta.Name] {
+		if !p.Active || !p.Installed {
 			a.plugins.DeactivatePlugin(p.Meta.Name)
 		}
 	}
 
+	a.plugins.InitRuntimes()
 	a.plugins.CallInitHooks()
 	a.plugins.StartSchedulers()
 	log.Print("[plugins] reload complete")
 	return nil
 }
+
+// InstallPlugin creates plugin's database tables and defaults via on_install hook.
+// Does NOT activate the plugin — use SetPluginEnabled after.
+func (a *App) InstallPlugin(name string) error {
+	if a.plugins == nil {
+		return fmt.Errorf("plugin manager not ready")
+	}
+	return a.plugins.Install(name)
+}
+
+// UninstallPlugin drops plugin's database tables and cleans data via on_uninstall hook.
+// Disables the plugin first if active. Does NOT delete plugin files from disk.
+func (a *App) UninstallPlugin(name string) error {
+	if a.plugins == nil {
+		return fmt.Errorf("plugin manager not ready")
+	}
+	return a.plugins.Uninstall(name)
+}