honor --timeout during mqtt connect handshake

[fabracht]

Summary

mqdb list --timeout 2 (and every other CLI command) didn't honor --timeout during the MQTT CONNECT handshake. connect_client in crates/mqdb-cli/src/common.rs only wrapped the request/response wait in tokio::time::timeout; the underlying MqttClient::connect[_with_options] calls had no timeout. Against a TCP listener that accepts the connection but never sends CONNACK (silent broker, half-open NAT, firewall drop after SYN-ACK), every command would hang indefinitely.

Reported repro: timeout 8 mqdb list ... --timeout 2 exits 124 against a silent listener but ~2.0s against a healthy broker.

The fix wraps the connect future in tokio::time::timeout(Duration::from_secs(conn.timeout), ...) and surfaces connect to {broker} timed out after {N}s on expiry. Affects every command that goes through connect_client (list, read, create, update, delete, schema, constraint, watch, etc.).

mqdb-cli 0.7.5 → 0.7.6.

Test plan

• cargo test -p mqdb-cli --test cli_test — 4 → 5 tests (one regression test added).
  • test_cli_connect_timeout_against_silent_listener spawns a std::net::TcpListener that accepts the connection without speaking MQTT, then asserts mqdb list ... --timeout 2 exits within 5s with a "timed out" error.
  • Verified to fail on main (pre-fix, exits at ~6s with "Connection reset by peer", missing "timed out") and pass with the fix (~2s).
• cargo make clippy — clean (pedantic, all targets + wasm).
• cargo make format-check — clean.
• Pre-commit hook (format-check + clippy) ran on the commit and passed.
• Manual repro against a Python silent listener: pre-fix, command hung past 8s (killed by timeout 8); post-fix, command exits in 2.018s with Error: "connect to 127.0.0.1:19999 timed out after 2s".
• cargo test (default features) — full workspace clean (no regressions). The mqtt-bridge-gated mqtt_transport_heartbeat_roundtrip integration test (deprecated transport per CLAUDE.md) is environmentally flaky on a hardcoded port 11883; not a regression from this PR.