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>

test/playnite.test.ts

@@ -0,0 +1,71 @@
+import { afterAll, describe, expect, test } from "bun:test";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { resolveConfig } from "../src/config.js";
+import { EXPORT_FILE } from "../src/export-schema.js";
+import { ExportError, locateExport, readExport } from "../src/playnite.js";
+
+const root = fs.mkdtempSync(path.join(os.tmpdir(), "pf-playnite-loc-"));
+afterAll(() => fs.rmSync(root, { recursive: true, force: true }));
+
+/** Lay out a fake Playnite data dir with an export under ExtensionsData/<guid>/. */
+const layout = (name: string, doc: unknown): string => {
+	const dir = path.join(root, name);
+	const ext = path.join(dir, "ExtensionsData", "abc-guid");
+	fs.mkdirSync(ext, { recursive: true });
+	if (doc !== undefined)
+		fs.writeFileSync(path.join(ext, EXPORT_FILE), JSON.stringify(doc));
+	return dir;
+};
+
+const validDoc = {
+	schema: 1,
+	generatedAt: "2026-01-01T00:00:00Z",
+	playnite: { version: "10", mode: "Desktop" },
+	games: [],
+};
+
+describe("locateExport", () => {
+	test("finds the export under an overridden Playnite dir", () => {
+		const dir = layout("found", validDoc);
+		const loc = locateExport(resolveConfig({ playniteDir: dir }));
+		expect(loc.dir).toBe(dir);
+		expect(loc.file).toBe(
+			path.join(dir, "ExtensionsData", "abc-guid", EXPORT_FILE),
+		);
+		expect(loc.mtime).toBeGreaterThan(0);
+	});
+
+	test("reports the dir but no file when the exporter hasn't written yet", () => {
+		const dir = path.join(root, "empty");
+		fs.mkdirSync(dir, { recursive: true });
+		const loc = locateExport(resolveConfig({ playniteDir: dir }));
+		expect(loc.dir).toBe(dir);
+		expect(loc.file).toBeNull();
+	});
+});
+
+describe("readExport", () => {
+	test("reads a valid export", () => {
+		const dir = layout("valid", validDoc);
+		const file = path.join(dir, "ExtensionsData", "abc-guid", EXPORT_FILE);
+		expect(readExport(file).schema).toBe(1);
+	});
+
+	test("rejects a future schema", () => {
+		const dir = layout("future", { ...validDoc, schema: 99 });
+		const file = path.join(dir, "ExtensionsData", "abc-guid", EXPORT_FILE);
+		expect(() => readExport(file)).toThrow(ExportError);
+	});
+
+	test("rejects non-JSON and foreign shapes", () => {
+		const bad = path.join(root, "bad.json");
+		fs.writeFileSync(bad, "{not json");
+		expect(() => readExport(bad)).toThrow(ExportError);
+
+		const foreign = path.join(root, "foreign.json");
+		fs.writeFileSync(foreign, JSON.stringify({ hello: "world" }));
+		expect(() => readExport(foreign)).toThrow(ExportError);
+	});
+});