fix(tests): stop committing node passwords + bound multinode RPC calls (§H)

- multinode suites no longer carry real node passwords as defaults: *_PW
  vars are required, auto-loaded from git-ignored tests/multinode/.env
  (lib sources it; .env.example documents the shape). Suites fail fast
  with a clear message when unset.
- node_login/node_rpc get --connect-timeout 10 --max-time 120 (override:
  MULTINODE_RPC_TIMEOUT) so one hung server-side RPC can't stall the whole
  suite. Verified live: login+rpc against .116 OK; unroutable node fails
  in 10s instead of hanging.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/multinode/.env.example

@@ -0,0 +1,15 @@
+# Local credentials for the multinode test suites — copy to tests/multinode/.env
+# (git-ignored) and fill in. Sourced automatically by lib/multinode.bash.
+# NEVER commit real node passwords.
+
+# smoke.sh / repro-federation-sync.sh
+A_PW=changeme            # node A (default URL http://192.168.1.116)
+B_PW=changeme            # node B (default URL https://192.168.1.228)
+#C_URL=https://x.x.x.x   # optional third node
+#C_PW=changeme
+
+# meshtastic.sh
+MA_PW=changeme
+MB_PW=changeme
+#MC_URL=https://x.x.x.x
+#MC_PW=changeme