feat: Playnite library sync plugin + exporter

A two-part Punktfunk plugin that syncs the Playnite library into the host
game library as the `playnite` provider:

- exporter/ — a minimal C# Playnite GenericPlugin ("Punktfunk Sync") that
  writes punktfunk-library.json on every library change. Reading Playnite's
  live-locked LiteDB from outside isn't robust, so this adapter runs inside
  Playnite. Builds net462 via reference assemblies; packaged as a .pext.
- src/ — the TS plugin (on @punktfunk/host, rom-manager shape): watches the
  export, embeds covers as data URLs, reconciles via
  PUT /library/provider/playnite, with a console-hosted web UI + standalone
  fallback + CLI. Launch = playnite://playnite/start/<id>, run by the host
  in the interactive session so Playnite performs the real launch.

Verified locally: backend tsc + 23 tests + biome clean, SPA build, C#
exporter build + .pext pack.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/paths.ts

@@ -0,0 +1,53 @@
+// 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.
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { fileURLToPath } from "node:url";
+
+/** The host's config dir — the same resolution the host and SDK use. */
+export const hostConfigDir = (): string => {
+	const explicit = process.env.PUNKTFUNK_CONFIG_DIR;
+	if (explicit) return explicit;
+	if (process.platform === "win32") {
+		const base = process.env.ProgramData ?? process.env.APPDATA ?? ".";
+		return path.join(base, "punktfunk");
+	}
+	const base =
+		process.env.XDG_CONFIG_HOME ?? path.join(os.homedir(), ".config");
+	return path.join(base, "punktfunk");
+};
+
+/** This plugin's private directory: `<config_dir>/playnite`. */
+export const pluginDir = (): string => path.join(hostConfigDir(), "playnite");
+
+/** `<config_dir>/playnite/config.json` — operator-editable, atomic-written. */
+export const configPath = (): string => path.join(pluginDir(), "config.json");
+
+/** `<config_dir>/playnite/cache.json` — disposable derived state (last reconcile fingerprint). */
+export const cachePath = (): string => path.join(pluginDir(), "cache.json");
+
+/**
+ * Locate the built SPA directory (`dist/ui`) at runtime. The package ships as ONE self-contained
+ * bundle so it installs from the Gitea registry with no external deps — which means `import.meta.url`
+ * can be `dist/index.js` (bundled) or `dist/server/index.js` (unbundled dev). We walk up from the
+ * calling module looking for a `ui/index.html`, so both layouts resolve. `fromUrl` is the caller's
+ * `import.meta.url`.
+ */
+export const resolveUiDir = (fromUrl: string): string => {
+	let dir = path.dirname(fileURLToPath(fromUrl));
+	for (let i = 0; i < 6; i++) {
+		for (const cand of [path.join(dir, "ui"), path.join(dir, "dist", "ui")]) {
+			try {
+				if (fs.existsSync(path.join(cand, "index.html"))) return cand;
+			} catch {
+				// keep walking
+			}
+		}
+		const parent = path.dirname(dir);
+		if (parent === dir) break;
+		dir = parent;
+	}
+	return path.join(path.dirname(fileURLToPath(fromUrl)), "ui");
+};