Fork xmrcheckout for Wownero (WOW)

Minimal changes from upstream xmrcheckout to support Wownero:
- Rate provider: Nonlogs WOW-BTC via Kraken BTC/USD
- Subaddress derivation: Wownero network byte overrides (53/63/54)
- Payment URI scheme: wownero:
- Dockerfile: Wownero binaries from Codeberg
- Display text: Monero→Wownero, XMR→WOW throughout UI
- Default daemon: 192.168.88.235:34568
- Added wownero-logo.svg

File and folder structure kept identical to upstream for easy sync.

api/app/subaddress_allocator.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+from sqlalchemy.orm import Session
+
+from .models import User
+from .security import decrypt_secret
+from .subaddress_derivation import derive_subaddress
+
+
+MAX_SUBADDRESS_INDEX = 100
+
+
+def create_subaddress_for_user(
+    db: Session,
+    *,
+    user: User,
+) -> tuple[str, int | None]:
+    locked = (
+        db.query(User)
+        .filter(
+            User.id == user.id,
+        )
+        .with_for_update()
+        .first()
+    )
+    if locked is None:
+        raise ValueError("User not found")
+    start_index = int(locked.subaddress_start_index or 0)
+    if start_index < 0 or start_index >= MAX_SUBADDRESS_INDEX:
+        start_index = 0
+    range_start = start_index + 1
+    range_end = MAX_SUBADDRESS_INDEX
+    next_index = int(locked.next_subaddress_index or range_start)
+    if next_index < range_start or next_index > range_end:
+        next_index = range_start
+    next_next_index = next_index + 1
+    if next_next_index > range_end:
+        next_next_index = range_start
+    locked.next_subaddress_index = next_next_index
+    db.flush()
+    view_key = decrypt_secret(locked.view_key_encrypted)
+    address = derive_subaddress(
+        payment_address=locked.payment_address,
+        view_key=view_key,
+        account_index=0,
+        address_index=next_index,
+    )
+    return address, int(next_index)