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)

contrib/plugins/calendar/main.lua

@@ -649,10 +649,9 @@ end
 -- Hooks
 --------------------------------------------------------------------------------
 
-function on_init()
-  print("Calendar: on_init — running migration")
+function on_install()
+  print("Calendar: on_install — creating tables")
 
-  -- Run migration SQL
   local ok, err = pcall(function()
     verstak.db.exec([[
       CREATE TABLE IF NOT EXISTS categories (
@@ -696,13 +695,40 @@ function on_init()
 
   if not ok then
     print("Calendar: migration error: " .. tostring(err))
+    error(err)
   else
     print("Calendar: migration complete")
   end
 
-  -- Ensure default categories
+  -- Insert default categories
   M.ensure_categories()
 
+  print("Calendar: install complete")
+end
+
+function on_uninstall()
+  print("Calendar: on_uninstall — dropping tables")
+
+  local ok, err = pcall(function()
+    verstak.db.exec("DROP TABLE IF EXISTS events")
+    verstak.db.exec("DROP TABLE IF EXISTS categories")
+  end)
+
+  if not ok then
+    print("Calendar: uninstall error: " .. tostring(err))
+  else
+    print("Calendar: tables dropped")
+  end
+
+  -- Clean up config
+  pcall(verstak.config.set, "categories", nil)
+
+  print("Calendar: uninstall complete")
+end
+
+function on_init()
+  print("Calendar: on_init — registering API")
+
   -- Register global API for panel access
   _G.calendar = M
 

contrib/plugins/calendar/plugin.json

@@ -7,7 +7,9 @@
 
   "hooks": {
     "on_init": "on_init",
-    "on_shutdown": "on_shutdown"
+    "on_shutdown": "on_shutdown",
+    "on_install": "on_install",
+    "on_uninstall": "on_uninstall"
   },
 
   "ui": {