feat: frontend Actions Tab with structured API, assign/create/remove dialogs (Task 3.3)

- ActionsTab rewritten with master/detail layout (mirrors FiltersTab)
- New AssignActionDialog and CreateActionDialog components
- ActionConfig type extended with active, used_by_jails, source_file, has_local_override
- New API functions: fetchActions, fetchAction, updateAction, createAction, deleteAction, assignActionToJail, removeActionFromJail
- useActionConfig updated to use new structured endpoints
- index.ts barrel exports updated

frontend/src/api/endpoints.ts

@@ -91,6 +91,10 @@ export const ENDPOINTS = {
     `/config/filters/${encodeURIComponent(name)}/parsed`,
   configJailFilter: (name: string): string =>
     `/config/jails/${encodeURIComponent(name)}/filter`,
+  configJailAction: (name: string): string =>
+    `/config/jails/${encodeURIComponent(name)}/action`,
+  configJailActionName: (jailName: string, actionName: string): string =>
+    `/config/jails/${encodeURIComponent(jailName)}/action/${encodeURIComponent(actionName)}`,
   configActions: "/config/actions",
   configAction: (name: string): string => `/config/actions/${encodeURIComponent(name)}`,
   configActionParsed: (name: string): string =>