feat: universal LLM gateway with embedded multilingual admin console

- OpenAI-compatible gateway with intelligent routing via cortiq-router (allaigate)
- Embedded build-free admin SPA at /admin: 7 languages (en/ru/de/fr/es/zh/tr),
  light/dark themes, hot config reload (no restart)
- Admin API, per-request statistics + Prometheus /metrics, secret store, playground
- English documentation (primary) with Russian translations (*.ru.md)

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

.gitignore

@@ -0,0 +1,10 @@
+/target
+**/*.rs.bk
+# Cargo.lock is committed: this is an application (binary), so we want reproducible builds.
+config/gateway.toml
+config/secrets.toml
+config/stats.jsonl
+config/*.toml.tmp
+.env
+*.log
+.DS_Store