fix(climate): support stateful split AC over MQTT IR blasters

[nesvet]

Summary

Fixes control of stateful split AC units through MQTT IR blasters (Zigbee2MQTT: Moes UFO-R11, ZS06, etc.).

Today SmartIR always sends a separate on IR packet before every mode/fan/temperature command. For stateful AC protocols the state packet already encodes power + mode + fan + setpoint. Sending on first causes many MQTT blasters to ignore the follow-up command or apply the wrong state.

This PR:

1. Skips the separate on command by default for MQTT controllers, while keeping the previous behaviour for Broadlink, Xiaomi, LOOK.in, and ESPHome.
2. Adds an explicit send_on_command YAML option (and optional per-device JSON field sendOnCommand) so users with hardware that still needs a dedicated power-on packet can opt back in.
3. Auto-formats MQTT payloads for Zigbee2MQTT:
   • topic ending in ir_code_to_send → raw code string
   • device set topic → {"ir_code_to_send":"<code>"}
   • command already JSON → passed through unchanged
4. Documents MQTT/Z2M setup in docs/CLIMATE.md.

Motivation / related issues

• Can't configure Moes UFO-R11 #1074 — Moes UFO-R11: direct mqtt.publish works, SmartIR does not (separate on + wrong payload format)
• Zigbee SmartIR ZS06 #873 — Zigbee SmartIR ZS06
• Community reports: stateful AC + MQTT works when only a single IR packet is sent per state change

Behaviour change

Controller	Before	After
MQTT	always sends on + state	sends state only (default)
Broadlink / others	sends on + state	unchanged

Backward compatibility: set send_on_command: true in YAML or "sendOnCommand": true in the device JSON.

Test plan

• MQTT + Z2M topic zigbee2mqtt/<device>/set/ir_code_to_send: climate.set_hvac_mode → climate.set_fan_mode → climate.set_temperature controls AC without a prior on packet
• MQTT + Z2M topic zigbee2mqtt/<device>/set: payload is valid JSON with ir_code_to_send
• send_on_command: true restores legacy on + state sequence on MQTT
• Broadlink climate entity still sends on before state commands (default unchanged)
• climate.turn_off still sends only the off command
• Entity attribute send_on_command reflects resolved setting

Example configuration

climate:
  - platform: smartir
    name: Kitchen AC
    device_code: 1962
    controller_data: zigbee2mqtt/Kitchen Smart IR Remote Control/set/ir_code_to_send
    # send_on_command defaults to false for MQTT; omit unless needed

Device JSON fields used with MQTT blasters:

{
  "supportedController": "MQTT",
  "commandsEncoding": "Raw"
}