admin: surface CMF worker threads + GPU toggle in Settings

Expose the two speed knobs in the /admin Settings panel instead of TOML-only:
- [cmf].gpu (new) -> exports CMF_GPU=1 to the managed cortiq serve (Metal/wgpu).
  On Apple Silicon decode is memory-bandwidth bound so this is ~neutral for
  generation (helps prefill); off by default.
- [cmf].threads (added earlier) now has a UI number input.

- config.rs: CmfCfg.gpu bool (serde default false).
- cmf_runtime.rs: spawn_serve sets CMF_GPU=1 when gpu is on.
- admin/mod.rs: put_settings flags needs_restart on threads/gpu change (the
  server is spawned once at startup with those env vars).
- settings.js: threads input + gpu checkbox + save payload + speed hint.
- i18n en/ru: threads/gpu/speedNote keys (other locales fall back to en, as the
  whole cmf section already does there).

web/js/i18n/en.js

@@ -239,6 +239,9 @@ export default {
   "settings.cmf.port": "Local server port",
   "settings.cmf.modelId": "Model id in the pool",
   "settings.cmf.note": "Serves a local .cmf via cortiq (github.com/infosave2007/cmf). Works even when the router is unavailable.",
+  "settings.cmf.threads": "Worker threads",
+  "settings.cmf.gpu": "Use GPU (Metal / wgpu)",
+  "settings.cmf.speedNote": "Threads parallelise the decode matvecs (~3x faster; 0 = runtime default). GPU offload mainly helps prefill of long prompts — decode is memory-bandwidth-bound, so on Apple Silicon it is roughly neutral.",
   "settings.router.taxonomy": "Taxonomy id",
   "settings.router.getKey": "Get or top up a router key at",
   "settings.router.secret": "Router key (value)",