fix(inbound): explain how to unlock fallbacks on the inbound form (#5014)

The fallbacks card only renders for VLESS/Trojan over RAW with TLS or
Reality security, and a new inbound starts at security=none — so the Add
Inbound page looked like it had lost fallback support entirely. Show an
inline hint in that state pointing at the Security tab.

internal/web/translation/en-US.json

@@ -282,7 +282,8 @@
         "quickAdded": "Added {n} fallback(s)",
         "quickAddedNone": "No new eligible inbounds to add",
         "routesWhen": "Routes when",
-        "defaultCatchAll": "Default — catches anything else"
+        "defaultCatchAll": "Default — catches anything else",
+        "needsTls": "Fallbacks become available once Security is set to TLS or Reality on the Security tab (VLESS/Trojan over RAW only)."
       },
       "protocol": "Protocol",
       "port": "Port",