fix: persist state under plugin-state/ (runner de-privilege)

The managed runner is de-privileged on Windows now (runs as LocalService),
and %ProgramData%\punktfunk is locked read-only to it — so writing config/
cache straight under the config dir fails EPERM. Move the plugin's state to
<config_dir>/plugin-state/playnite, which `punktfunk-host plugins enable`
grants the runner write on. On Linux the runner owns the config dir, so the
path is writable there too. First release, so no migration needed.

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

src/paths.ts

@@ -1,6 +1,6 @@
 // Where the plugin's own files live. The host config-dir resolution mirrors the SDK's `configDir`
 // (`@punktfunk/host` does not re-export it) so we always land in the same place the host and runner
-// use; the plugin owns a `playnite/` subtree under it, created 0700.
+// use; the plugin owns a `plugin-state/playnite/` subtree under it, created 0700.
 import * as fs from "node:fs";
 import * as os from "node:os";
 import * as path from "node:path";
@@ -19,8 +19,18 @@ export const hostConfigDir = (): string => {
 	return path.join(base, "punktfunk");
 };
 
-/** This plugin's private directory: `<config_dir>/playnite`. */
-export const pluginDir = (): string => path.join(hostConfigDir(), "playnite");
+/**
+ * This plugin's private directory: `<config_dir>/plugin-state/playnite`.
+ *
+ * The state lives under `plugin-state/`, not straight under the config dir, because the managed
+ * runner is de-privileged on Windows (`NT AUTHORITY\LocalService`) and the config dir is locked
+ * read-only there — `punktfunk-host plugins enable` grants the runner write on exactly
+ * `plugin-state`. (Mirrors `@punktfunk/host`'s `pluginStateDir`; reimplemented locally like
+ * `hostConfigDir`, since we don't gate on an SDK version bump.) On Linux the runner owns the config
+ * dir, so the same path is writable with no special step.
+ */
+export const pluginDir = (): string =>
+	path.join(hostConfigDir(), "plugin-state", "playnite");
 
 /** `<config_dir>/playnite/config.json` — operator-editable, atomic-written. */
 export const configPath = (): string => path.join(pluginDir(), "config.json");