feat: Pump control and water cooling support

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Feature Description

Add dedicated support for water cooling pumps and AIO coolers.

Motivation

Pumps have different requirements than fans:

• Constant speed operation preferred
• Lower PWM frequencies (10-15 kHz)
• Flow rate monitoring
• Coolant temperature critical

Features

Pump Mode per Channel

pico-fan-ctl config channel 6 --mode pump --pwm-freq 12

Pump Mode Characteristics:

• Default speed: 80% (not 0%)
• Minimum speed: 40% (prevent cavitation)
• Slower ramp rates
• Alarm on low RPM

Coolant Temperature Integration

• Dedicated sensor for coolant temp
• Most critical temperature
• Primary input for fan curves

Flow Rate Monitoring

• Calculate from pump tach signal
• Flow rate = RPM × pump factor
• Alert on low flow
• Exposure via hwmon

Safety Features

• Never stop pump (minimum speed)
• Alarm on pump failure
• All fans → 100% if pump fails
• Buzzer alert

Hardware

No changes required:

• Use existing fan connectors
• Same tach reading
• PWM frequency adjustable

Optional additions:

• Dedicated pump connectors (3-pin)
• Flow meter support (pulse counting)

Software

hwmon

pump1_input  # Pump RPM
flow1_input  # Flow rate (L/h)
temp1_input  # Coolant temperature

CLI

pico-fan-ctl pump status
pico-fan-ctl pump set-speed 80
pico-fan-ctl pump curve --based-on coolant_temp

Priority

Medium - Important for water cooling users