M6-T05: add Tibber GraphQL client + price refresh service + schedule

- app/integrations/tibber/client.py: fetch_price_range/fetch_current_price
  (priceInfoRange QUARTER_HOURLY, startsAt->UTC, no fixed node count assumption),
  TibberError/TibberAuthError; token never logged or put in exception text.
- app/services/tibber_prices.py: refresh_prices upserts by starts_at (idempotent),
  no-op unless an active kind=tibber contract + token exist.
- main.py: hourly tibber-refresh job (existing jobs/MQTT untouched). Tests added.

app/services/tibber_prices.py

@@ -0,0 +1,139 @@
+"""Service layer for fetching and persisting Tibber 15-minute electricity prices.
+
+``refresh_prices`` is the main entry point.  It is designed to be called from a
+scheduled background job (see ``app/main.py``) and from tests.
+
+Design decisions
+----------------
+- **Guard clause**: if no active contract with ``kind="tibber"`` exists, or if
+  the Tibber API token is empty in the runtime settings, the function is a
+  complete no-op (returns 0) and does not raise.  This means the scheduler can
+  call ``refresh_prices`` unconditionally; the service itself decides whether to
+  do anything based on current configuration.
+- **Upsert idempotency**: rows are matched by ``starts_at`` (the unique
+  constraint on ``tibber_price``).  If a row already exists, its price fields
+  and ``fetched_at`` are updated in-place; if it does not exist, a new row is
+  inserted.  Running ``refresh_prices`` twice in a row must not double-insert.
+- **No destructive operations**: this service never deletes ``tibber_price``
+  rows.  Only INSERT or UPDATE.
+- **Exception propagation**: exceptions from the Tibber client are *not*
+  swallowed here.  The scheduled job wrapper in ``main.py`` is responsible for
+  catching and logging errors so that a single fetch failure does not crash the
+  scheduler.
+- **SQLite timezone note**: ``DateTime(timezone=True)`` columns come back as
+  timezone-naive UTC datetimes on read.  We store UTC-aware datetimes on write
+  (``starts_at`` from ``PricePoint`` is already UTC-aware; ``fetched_at`` is
+  ``datetime.now(UTC)``).  Reads elsewhere that compare against these values
+  must normalise accordingly.
+"""
+
+from __future__ import annotations
+
+import logging
+from datetime import UTC, datetime
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+
+from app.integrations.tibber.client import fetch_price_range
+from app.models.energy import EnergyContract, TibberPrice
+
+logger = logging.getLogger(__name__)
+
+
+def _active_tibber_contract_exists(session: Session) -> bool:
+    """Return True if there is an active contract with kind='tibber'."""
+    row = session.execute(
+        select(EnergyContract).where(
+            EnergyContract.active.is_(True),
+            EnergyContract.kind == "tibber",
+        ).limit(1)
+    ).scalar_one_or_none()
+    return row is not None
+
+
+def refresh_prices(session: Session, settings: object) -> int:
+    """Fetch today-and-tomorrow Tibber prices and upsert them into ``tibber_price``.
+
+    Parameters
+    ----------
+    session:
+        An active SQLAlchemy session.  The caller is responsible for closing it;
+        this function commits each upserted row individually to keep transactions
+        short.
+    settings:
+        A runtime settings object that exposes ``tibber_api_token`` and
+        ``tibber_home_id`` attributes (typically a ``Settings`` or merged
+        runtime-settings instance from ``build_runtime_settings``).
+
+    Returns
+    -------
+    int
+        Number of rows upserted (inserted or updated).  Returns 0 for a no-op.
+
+    Notes
+    -----
+    - No-op (returns 0) when:
+        * No active contract exists with ``kind="tibber"``, OR
+        * ``settings.tibber_api_token`` is empty or whitespace.
+    - Exceptions from the Tibber client are *not* caught here; they propagate to
+      the caller (the scheduled job wrapper swallows them and logs).
+    """
+    token: str = getattr(settings, "tibber_api_token", "") or ""
+    if not token.strip():
+        logger.debug("refresh_prices: tibber_api_token is empty — no-op")
+        return 0
+
+    if not _active_tibber_contract_exists(session):
+        logger.debug("refresh_prices: no active tibber contract — no-op")
+        return 0
+
+    home_id: str = getattr(settings, "tibber_home_id", "") or ""
+    home_id_or_none: str | None = home_id.strip() or None
+
+    logger.info("refresh_prices: fetching Tibber price range (home_id=%r)", home_id_or_none)
+
+    # May raise TibberError or TibberAuthError — let them propagate.
+    price_points = fetch_price_range(token, home_id_or_none)
+
+    if not price_points:
+        logger.info("refresh_prices: API returned zero price points — nothing to upsert")
+        return 0
+
+    fetched_at = datetime.now(UTC)
+    upserted = 0
+
+    for point in price_points:
+        existing = session.execute(
+            select(TibberPrice).where(TibberPrice.starts_at == point.starts_at)
+        ).scalar_one_or_none()
+
+        if existing is not None:
+            # Update in-place — price fields may change (e.g. Tibber corrects a
+            # forecast), but starts_at and resolution stay the same.
+            existing.total = point.total
+            existing.energy = point.energy
+            existing.tax = point.tax
+            existing.level = point.level
+            existing.currency = point.currency
+            existing.fetched_at = fetched_at
+        else:
+            session.add(
+                TibberPrice(
+                    starts_at=point.starts_at,
+                    resolution=point.resolution,
+                    total=point.total,
+                    energy=point.energy,
+                    tax=point.tax,
+                    level=point.level,
+                    currency=point.currency,
+                    fetched_at=fetched_at,
+                )
+            )
+
+        upserted += 1
+
+    session.commit()
+
+    logger.info("refresh_prices: upserted %d price points", upserted)
+    return upserted