feat(security): give the de-privileged runner a writable plugin-state dir

The LocalService runner cannot write anywhere under %ProgramData%\punktfunk
(the config dir is Users-read-only), so a state-writing plugin's saveCache /
config-edit / first-run mkdir all fail EPERM — proven on-glass (rom-manager
only looked fine because its state dir was pre-created by an admin run and a
0-title reconcile skipped the write).

Add the one writable grant the model was missing, keeping the split crisp —
code dirs RX+WA, secrets R, and now a dedicated state root RW:

- plugins enable / build-scripting.ps1: create %ProgramData%\punktfunk  plugin-state and grant LocalService (OI)(CI)(M); disable revokes. Users stay
  read-only, so another non-admin still can't tamper with a plugin's launch
  templates.
- SDK: export pluginStateDir(name) -> <config_dir>/plugin-state/<name>. Same
  path on Linux (the systemd --user runner owns the config dir, writable with
  no grant), so plugins use one branch-free helper.

Plugins must persist under pluginStateDir(), not straight under the config dir.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

sdk/src/index.ts

@@ -30,6 +30,8 @@ import {
 export type { HostApi } from "./api.js";
 export { HttpStatusError } from "./core.js";
 export type { ConnectOptions } from "./config.js";
+// A plugin persists its state here — the one dir the de-privileged Windows runner may write.
+export { pluginStateDir } from "./config.js";
 export {
 	type PluginUiHandle,
 	type PluginUiOptions,