fix(mesh): route ordering shadowed /api/mesh/register; initiator side never got a self-entry

Two real bugs found while live-testing the new GET /api/mesh/self
endpoint with two actual jump-host containers (mesh-joined for real,
not mocked):

1. routes/api.js mounted `/` (routes/jump.js, admin-session-gated)
   before `/mesh`. Since router.use('/', ...) matches every /api/*
   path, EVERY /api/mesh/* request -- including /register, which is
   authenticated by a bearer mesh join token, not an admin session --
   hit that admin gate first and 401'd before routes/mesh.js ever ran.
   Confirmed live: a real gateway-to-gateway /join call failed with a
   checkApiToken/LoginFailed error instead of ever reaching /register.
   Reordered so /mesh is mounted first.

2. POST /register (the receiving side of a join) persists a `(self)`
   registry entry via ensureOwnMeshIndex(), but POST /join (the
   initiating side) never did -- so GET /api/mesh/self and the mesh
   UI's own-entry handling silently saw nothing on whichever gateway
   called /join. Fixed by registering a self-entry there too, using
   the exact meshIndex the remote assigned (models/mesh_gateway.js's
   register() now accepts an explicit meshIndex instead of always
   auto-picking one from the local registry, which has no reason to
   agree with what's actually configured on the live wg0 interface).

Verified with two real containers joined over a live network: both
sides now report their own correct mesh IP via GET /api/mesh/self,
and both appear correctly in GET /api/mesh/gateways.

nodejs/routes/api.js

@@ -13,15 +13,21 @@ router.use('/user', middleware.auth, require('./user'));
 // admin gate (see routes/api_token.js for why a token can't reach admin routes).
 router.use('/api-token', middleware.auth, require('./api_token'));
 
-// Jump-host data — jump admin only (audit log, active sessions, metrics).
-router.use('/', middleware.auth, middleware.requireJumpAdmin, require('./jump'));
-
 // WireGuard peer + site management — admin only.
 router.use('/wireguard', middleware.auth, middleware.requireJumpAdmin, require('./wireguard'));
 
 // Gateway-to-gateway mesh — mixed auth (register/register-* are called by a
 // remote gateway with a bearer join token, not an admin session; join-tokens
 // mint + join are admin-gated). See routes/mesh.js for the per-route gates.
+// MUST be registered before the '/' mount below: '/' matches every /api/*
+// path (it's the catch-all for routes/jump.js), so registering it first
+// would shadow every /api/mesh/* route with admin-session auth before
+// routes/mesh.js's own per-route gates ever ran -- confirmed live, this
+// silently 401'd /register's bearer-join-token callers with a
+// checkApiToken/LoginFailed error instead of ever reaching mesh.js.
 router.use('/mesh', require('./mesh'));
 
+// Jump-host data — jump admin only (audit log, active sessions, metrics).
+router.use('/', middleware.auth, middleware.requireJumpAdmin, require('./jump'));
+
 module.exports = router;