feat: initial ROM & emulator manager plugin (M0–M5)

A punktfunk-plugin-* package that scans ROM directories, maps them to
emulators, fetches box art, and reconciles them into the host game library
under provider id `rom-manager` — with a console-hosted web UI.

Engine (pure, unit-tested core):
- Table-driven platform registry (~25 consoles) + emulator registry with
  best-effort per-OS detection (PATH / Flatpak / known paths) and RetroArch
  core discovery.
- Scanner with disc folding (m3u/cue/gdi), archive gating, excludes.
- No-Intro title parsing + optional per-platform region dedupe.
- Security-critical quoting seam: POSIX single-quote + Windows double-quote
  with hostile-name refusal; ROM filenames never reach a shell un-quoted.
- Pure desired-state reconcile (stable external_ids, scale guard, fingerprint
  skip) → full-replace PUT /library/provider/rom-manager.

Box art (like Steam ROM Manager): SteamGridDB primary (portrait/hero/logo/
header, fuzzy match, operator API key) behind a provider seam, with keyless
libretro-thumbnails as the zero-setup fallback (`auto` default).

UI: console-hosted via the SDK `servePluginUi` (zero plugin-side auth) with a
plugin-local REST/SSE API and a self-contained React SPA (Setup / Emulators /
Games / Sync). Standalone password-gated fallback for host-only installs.

CLI: scan / detect / preview / sync / uninstall / set-password.

48 engine tests, typecheck + biome clean, SPA builds. Verified end-to-end:
scan → detect → reconcile PUT, fingerprint idempotence, and the standalone
UI serving SPA + REST.

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

src/paths.ts

@@ -0,0 +1,28 @@
+// 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 `rom-manager/` subtree under it (design §9), created 0700.
+import * as os from "node:os";
+import * as path from "node:path";
+
+/** 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>/rom-manager`. */
+export const pluginDir = (): string =>
+	path.join(hostConfigDir(), "rom-manager");
+
+/** `<config_dir>/rom-manager/config.json` — operator-editable, atomic-written. */
+export const configPath = (): string => path.join(pluginDir(), "config.json");
+
+/** `<config_dir>/rom-manager/cache.json` — disposable derived state (art verdicts, detection, fingerprint). */
+export const cachePath = (): string => path.join(pluginDir(), "cache.json");