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.

package.json

@@ -9,10 +9,10 @@
     "build": "next build --webpack",
     "postbuild": "node scripts/copy-standalone-assets.mjs",
     "postbuild:bun": "node scripts/copy-standalone-assets.mjs",
-    "start": "next start --port 20127",
+    "start": "node custom-server.js --port 20127",
     "dev:bun": "bun --bun next dev --webpack --port 20127",
     "build:bun": "bun --bun next build --webpack",
-    "start:bun": "bun ./.next/standalone/server.js",
+    "start:bun": "bun ./.next/standalone/custom-server.js",
     "cli:pack": "npm --prefix cli run pack:cli",
     "cli:publish": "npm --prefix cli run publish:cli"
   },