docs(tunnel-node): add Persian translation of README (#372)

Mirror of the English README with the same setup paths (Cloud Run /
Docker prebuilt / Docker source / direct binary), env-var table, and
protocol section, plus a Persian-language FAQ section answering the
specific questions users keep filing:

- bandwidth overhead (~25-30% from base64 + JSON envelope + v1.8.0
  random padding)
- whether all Android apps get tunneled (yes in Tunnel mode + VpnService;
  no in Proxy mode)
- realistic per-flow throughput (~50-200 KB/s, bound by Apps Script's
  per-roundtrip floor; horizontal-scale via more deployments)
- whether a VPS is required for Full mode (yes; not required for
  apps_script or google_only)
- which VPS to pick (Hetzner CX11 €4/mo for general use; Cloud Run
  free tier specifically for Iran users hit by #313 since destination
  IP stays Google-internal)

Adds an `MHRV_DIAGNOSTIC` env-var row to both the English and Persian
env-var tables — was added in v1.8.0 but never documented.

Closes #372.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tunnel-node/README.md

@@ -1,5 +1,7 @@
 # Tunnel Node
 
+> *Persian / فارسی: [README.fa.md](./README.fa.md)*
+
 HTTP tunnel bridge server for MasterHttpRelayVPN "full" mode. Bridges HTTP tunnel requests (from Apps Script) to real TCP connections.
 
 ## Architecture