Add support for inverter current caps in site configuration

- Introduced `InverterModbusCurrentCapsBody` model for updating max charge and discharge currents.
- Updated SQL queries to utilize `COALESCE` for effective current limits.
- Modified relevant tests to reflect changes in battery current handling.
- Added new SQL migration for `deye_register_max_current_a` columns in the database.

backend/app/routers/site_configuration.py

@@ -7,12 +7,24 @@ from typing import Annotated, Any
 
 import asyncpg
 from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel, Field
 
 from app.db_json import record_to_dict
 from app.deps import get_pg_pool
 
 router = APIRouter(prefix="/sites/{site_id}", tags=["sites"])
 
+
+class InverterModbusCurrentCapsBody(BaseModel):
+    """Tvrdý strop proudu pro zápis Deye reg 108/109 (A); NULL ve JSONu = smaž strop v DB."""
+
+    deye_register_max_charge_a: int | None = Field(
+        default=None, ge=0, le=640, description="None při vynechání klíče = nezměnit; explicitní null = smazat strop"
+    )
+    deye_register_max_discharge_a: int | None = Field(
+        default=None, ge=0, le=640, description="Jako u nabíjení"
+    )
+
 _DEYE_KEYS = frozenset(
     {
         "deye_last_system_time_sync_at",
@@ -246,3 +258,71 @@ async def get_site_configuration(
             "active_plan_created_at": _iso_utc(run_row["created_at"]) if run_row else None,
         },
     }
+
+
+@router.patch("/inverters/{inverter_id}/modbus-current-caps")
+async def patch_inverter_modbus_current_caps(
+    site_id: int,
+    inverter_id: int,
+    body: InverterModbusCurrentCapsBody,
+    pool: Annotated[asyncpg.Pool, Depends(get_pg_pool)],
+) -> dict[str, Any]:
+    """
+    Nastavení `deye_register_max_charge_a` / `deye_register_max_discharge_a` na `ems.asset_inverter`.
+    Hodnoty se uplatní v dotazu `_load_inverter_config` jako `COALESCE(strop_A, FLOOR(…z_kW))` pro reg 108/109.
+    """
+    updates = body.model_dump(exclude_unset=True)
+    if not updates:
+        raise HTTPException(
+            status_code=400,
+            detail="Send at least one of: deye_register_max_charge_a, deye_register_max_discharge_a",
+        )
+    async with pool.acquire() as conn:
+        owner = await conn.fetchval(
+            """
+            SELECT id FROM ems.asset_inverter
+            WHERE id = $1 AND site_id = $2
+            """,
+            inverter_id,
+            site_id,
+        )
+        if owner is None:
+            raise HTTPException(status_code=404, detail="Inverter not found for this site")
+
+        sets: list[str] = []
+        args: list[Any] = []
+        n = 1
+        if "deye_register_max_charge_a" in updates:
+            sets.append(f"deye_register_max_charge_a = ${n}")
+            args.append(updates["deye_register_max_charge_a"])
+            n += 1
+        if "deye_register_max_discharge_a" in updates:
+            sets.append(f"deye_register_max_discharge_a = ${n}")
+            args.append(updates["deye_register_max_discharge_a"])
+            n += 1
+
+        args.extend([inverter_id, site_id])
+        await conn.execute(
+            f"""
+            UPDATE ems.asset_inverter
+            SET {", ".join(sets)}
+            WHERE id = ${n} AND site_id = ${n + 1}
+            """,
+            *args,
+        )
+        row = await conn.fetchrow(
+            """
+            SELECT id, code, deye_register_max_charge_a, deye_register_max_discharge_a
+            FROM ems.asset_inverter
+            WHERE id = $1 AND site_id = $2
+            """,
+            inverter_id,
+            site_id,
+        )
+    assert row is not None
+    return {
+        "inverter_id": int(row["id"]),
+        "code": row["code"],
+        "deye_register_max_charge_a": row["deye_register_max_charge_a"],
+        "deye_register_max_discharge_a": row["deye_register_max_discharge_a"],
+    }