Add Tuya Cloud integration; 2-step add-board wizard; DP value formatting

- Tuya Cloud Gateway driver (tuya-device-sharing-sdk):
  - QR-code auth flow: user-provided user_code, terminal_id/endpoint
    returned by Tuya login_result (mirrors HA implementation)
  - Device sync, toggle DP, rename, per-device detail page
  - category → kind mapping; detect_switch_dps helper
  - format_dp_value: temperature (÷10 + °C/°F), humidity (+ %)
    registered as 'tuya_dp' Jinja2 filter

- TuyaDevice model (tuya_devices table)

- Templates:
  - tuya/gateway.html: device grid with live-reading sensor cards
    (config/threshold keys hidden from card, shown on detail page)
  - tuya/device.html: full status table with formatted DP values
  - tuya/auth_settings.html: user_code input + QR scan flow

- Add-board wizard refactored to 2-step flow:
  - Step 1: choose board type (Cloud Gateways vs Hardware)
  - Step 2: type-specific fields; gateways skip IP/relay fields

- Layout builder: Tuya chip support (makeTuyaChip, tuya_update socket)

- requirements.txt: tuya-device-sharing-sdk, cryptography

app/models/board.py

@@ -56,6 +56,10 @@ class Board(db.Model):
         "SonoffDevice", back_populates="board",
         cascade="all, delete-orphan", lazy="dynamic"
     )
+    tuya_devices = db.relationship(
+        "TuyaDevice", back_populates="board",
+        cascade="all, delete-orphan", lazy="dynamic"
+    )
 
     # ── helpers ──────────────────────────────────────────────────────
     @property