v0.9.0

• Raw MQTT passthrough: new mqtt command group — mqtt publish,
  mqtt read, mqtt watch, mqtt topics. z2m's control surface is MQTT:
  bridge request/response topics, per-device <name>/set and <name>/get
  writes, and retained state dumps. Every command until now went through a
  typed wrapper; these four reach anything the wrappers don't model — a
  payload key no convenience command covers, a retained dump
  (bridge/info, bridge/devices, a device's state topic), an MQTT
  wildcard tail, or a future/tweaked bridge API the moment z2m ships it —
  without leaving the CLI.
  • mqtt publish <topic> [payload] — topic resolves against the base
    topic (lamp/set → zigbee2mqtt/lamp/set; a topic that already starts
    with the base topic is used verbatim). A payload string that parses as
    JSON is sent as JSON (so the wire is indistinguishable from
    device set); any other text is published verbatim; an omitted payload
    publishes an empty message. --retain and --qos 0-2 set the MQTT
    flags; bad values abort before any broker connection. Output
    {"topic", "payload", "published", "rc", "retain", "qos"} — gate
    scripts on published/rc like device identify.
  • mqtt read <topic> [--timeout S] — one-shot retained read, JSON-decoded
    when possible. payload: null means "nothing ever published on this
    topic" — a valid answer, not an error, and the fastest way to read any
    retained z2m dump.
  • mqtt watch <filter> [--duration S] — collect every message matching an
    MQTT wildcard filter (e.g. sensor1/#, bridge/logging) for
    --duration seconds (default 15, Ctrl-C stops early); consumer-callback
    errors are logged, never fatal (same contract as bridge watch-events).
  • mqtt topics [--prefix P] [--duration S] — enumerate the topics under
    <base>/#: subscribing pulls every retained dump in immediately, so a
    short default window (2s) snapshots the whole topic tree with payload
    size and a truncated preview per row — topic discovery without knowing
    names up front.
• Core functions normalize_topic, coerce_payload, check_qos,
  publish_raw, read_raw, watch_topic, list_topics in the new
  core/mqtt_raw.py; the topic-resolution and payload-coercion helpers are
  client-free, like the rest of the introspection helpers.
• Bug fix riding along: every watch loop (mqtt watch, bridge watch-events / watch-logging, device watch) treated --duration 0 as
  "tail forever" — time.time() + duration if duration else None is falsy
  on 0 — so a zero-width window hung the CLI. All four now use
  duration is not None; --duration 0 is a non-blocking drain.
• Why it matters: the typed groups are coverage, not a cage. When z2m adds or
  changes a bridge API, mqtt publish / mqtt read works against it the
  same minute; and one-off payloads that no convenience command models are a
  one-liner instead of a second MQTT tool. Recommended loop: mqtt topics
  to discover, mqtt read to inspect, mqtt publish to act, mqtt watch
  to confirm.
• 64 new tests (40 unit + 24 E2E/workflow); total suite 1055 passed, gate
  green (coverage 99.15%, ruff check/format clean, bandit clean).