mobile: add a phone dashboard on a second port (8443) — Live + Archive

A new mobile dashboard is served on a second host port (8443) mapped to the
same backend, so the recorder/supervisor is not duplicated. main.py detects
the mobile port via the Host header and serves mobile.html instead of the
desktop index. The mobile SPA has two modes: Live (one camera with a selector)
and Archive (camera + date + segment list). Video is delivered as server-side
H.264 (live.mp4 / play.mp4 transcode) so a plain <video> plays on any phone.
Bottom tab bar, dark theme, safe-area aware.

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

backend/app/main.py

@@ -28,6 +28,13 @@ logging.basicConfig(
 log = logging.getLogger("nvr")
 
 FRONTEND_DIR = os.path.join(os.path.dirname(__file__), "..", "frontend")
+# Мобильный dashboard: тот же бэкенд слушает один порт, но в docker проброшен второй
+# хост-порт (8443→8090). Запрос на него приходит с Host ".. :8443" → отдаём mobile.html.
+MOBILE_PORT = os.environ.get("NVR_MOBILE_PORT", "8443")
+
+
+def _is_mobile(request: Request) -> bool:
+    return request.headers.get("host", "").endswith(":" + MOBILE_PORT)
 
 
 @asynccontextmanager
@@ -109,8 +116,10 @@ app.include_router(ws.router)
 
 # ── фронтенд ────────────────────────────────────────────────────
 @app.get("/")
-async def index() -> FileResponse:
-    return FileResponse(os.path.join(FRONTEND_DIR, "index.html"))
+async def index(request: Request) -> FileResponse:
+    # на мобильном порту — мобильный dashboard (Live одной камеры + Архив)
+    page = "mobile.html" if _is_mobile(request) else "index.html"
+    return FileResponse(os.path.join(FRONTEND_DIR, page))
 
 
 @app.get("/archive")