feat: add built-in gpio-control skill for switch confirmation

spiffs_data/skills/gpio-control.md

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+# GPIO Control
+
+Control and monitor GPIO pins on the ESP32-S3 for digital I/O.
+
+## When to use
+When the user asks to:
+- Turn on/off LEDs, relays, or other outputs
+- Check switch states, button presses, or sensor readings
+- Confirm digital I/O status (switch confirmation)
+- Get an overview of all GPIO pin states
+
+## How to use
+1. To **read a switch/sensor**: use gpio_read with the pin number
+   - Returns HIGH (1) or LOW (0)
+   - HIGH typically means switch is ON / circuit closed
+   - LOW typically means switch is OFF / circuit open
+2. To **set an output**: use gpio_write with pin and state (1=HIGH, 0=LOW)
+3. To **scan all pins**: use gpio_read_all for a full status overview
+4. For **switch confirmation**: read the pin, report state, optionally toggle and re-read to verify
+
+## Pin safety
+- Only pins within the allowed range can be accessed
+- ESP32 flash pins (6-11) are always blocked
+- If a pin is rejected, suggest an alternative within the allowed range
+
+## Example
+User: "Check if the switch on pin 4 is on"
+→ gpio_read {"pin": 4}
+→ "Pin 4 = HIGH"
+→ "The switch on pin 4 is currently ON (HIGH)."
+
+User: "Turn on the relay on pin 5"
+→ gpio_write {"pin": 5, "state": 1}
+→ "Pin 5 set to HIGH"
+→ gpio_read {"pin": 5}
+→ "Pin 5 = HIGH"
+→ "Relay on pin 5 is now ON. Confirmed HIGH."