fix(security): require proof that x-9r-real-ip came from the socket (GHSA-pjm4-8fpg-f9p6)

x-9r-real-ip and the Host fallback were trusted from client-controlled
headers whenever custom-server.js was not in the request path (npm run
start, start:bun), letting a remote caller pose as local to skip API key
auth and reach LOCAL_ONLY_PATHS (/api/mcp/*, /api/tunnel/enable,
/api/auth/reset-password).

custom-server.js now generates a per-process secret at boot and stamps it
as x-9r-peer-token on every request it sanitizes. hasTrustedPeerHeaders()
(src/lib/auth/trustedPeer.js) gates trust in x-9r-real-ip on that secret;
otherwise the guard falls back to Host only in development, and fails
closed in production. Same gate on loginLimiter.getClientIp() so a spoofed
header cannot rotate the login lockout bucket.

Also: fix isLoopbackHostname for IPv6 (::1, ::ffff:127.0.0.1) which the
old split(":")[0] reduced to empty string; route npm run start /
start:bun through custom-server.js (postbuild copies it into
.next/standalone, build-cli.js fails without it) so documented deployments
keep passwordless local access.

custom-server.js

@@ -1,9 +1,18 @@
 const http = require("http");
 const path = require("path");
+const fs = require("fs");
+const crypto = require("crypto");
 const { pathToFileURL } = require("url");
 
 const origCreate = http.createServer.bind(http);
 
+// Per-process secret proving x-9r-real-ip was stamped below rather than sent by the client.
+// A bare `next start` / `next dev` never loads this file, so it cannot produce a matching
+// header even though the env var is inherited by child processes. Named like x-9r-cli-token
+// so the request-detail header sanitizer redacts it too.
+const PEER_TOKEN = crypto.randomBytes(24).toString("hex");
+process.env.NINEROUTER_PEER_TOKEN = PEER_TOKEN;
+
 let backgroundRefreshStarted = false;
 
 function startBackgroundTokenRefreshFromCustomServer() {
@@ -57,7 +66,9 @@ http.createServer = (...args) => {
     delete req.headers["x-9r-real-ip"];
     delete req.headers["x-forwarded-for"];
     delete req.headers["x-9r-via-proxy"];
+    delete req.headers["x-9r-peer-token"];
     req.headers["x-9r-real-ip"] = ip;
+    req.headers["x-9r-peer-token"] = PEER_TOKEN;
     if (viaProxy) req.headers["x-9r-via-proxy"] = "1";
     return handler(req, res);
   };
@@ -114,4 +125,15 @@ http.createServer = (...args) => {
   return server;
 };
 
-if (require.main === module) require("./server.js");
+if (require.main === module) {
+  const standalone = path.join(__dirname, "server.js");
+  if (fs.existsSync(standalone)) {
+    require(standalone);
+  } else {
+    // Repo checkout has no standalone build next to us. `next start` builds its HTTP
+    // server in-process, so the wrapper above still sanitizes every request.
+    const nextBin = require.resolve("next/dist/bin/next");
+    process.argv = [process.argv[0], nextBin, "start", ...process.argv.slice(2)];
+    require(nextBin);
+  }
+}