feat(service-storage-harness): slice 1 — harness + qbit store + client + integration

ServiceDataHarness (services/service_data.py): lifecycle-only registry of
per-concern storage — DB provisioning, idempotent migrations (ALTER TABLE
duplicate-column-name caught per-statement), cascade_delete(service_id).
QbittorrentSampleStore: append/window/prune (MAX_SAMPLES=120) in
qbittorrent.db. QbittorrentClient: cookie-login Web API client (403 re-login,
/sync/maindata). Integration registered with 3 widget kinds (totals/active/
speed). Harness initialized in main.py lifespan.

Backend: 314 pytest pass (21 new), ruff clean.

backend/src/media_library_viewer_api/integrations/qbittorrent.py

@@ -0,0 +1,68 @@
+"""qBittorrent service definition.
+
+Declares the config model (base URL + timeout), secret fields (username +
+password), and three widget kinds (totals, active, speed). Models on
+:mod:`media_library_viewer_api.integrations.prometheus`.
+"""
+
+from __future__ import annotations
+
+from media_library_viewer_api.integrations.base import (
+    SecretField,
+    ServiceBaseUrl,
+    ServiceConfigBase,
+    ServiceDefinition,
+    WidgetConfigBase,
+    widget_kind,
+)
+
+
+class QbittorrentConfig(ServiceConfigBase):
+    """Non-secret qBittorrent connection config."""
+
+    base_url: ServiceBaseUrl
+    timeout_seconds: int = 10
+
+
+class QbittorrentWidgetConfig(WidgetConfigBase):
+    """Per-widget config (empty — all three kinds derive from the service connection)."""
+
+    pass
+
+
+DEFINITION = ServiceDefinition(
+    service_type="qbittorrent",
+    name="qBittorrent",
+    description="Torrent client activity, speeds, and item counts.",
+    config_model=QbittorrentConfig,
+    secret_fields=[
+        SecretField(key="username", label="Username", required=True),
+        SecretField(key="password", label="Password", required=True, helper="Stored encrypted"),
+    ],
+    widget_kinds=[
+        widget_kind(
+            kind="totals",
+            name="Totals",
+            description="Count of all listed torrents, broken down by state.",
+            model_cls=QbittorrentWidgetConfig,
+            default_config={},
+            refresh_interval_ms=30_000,
+        ),
+        widget_kind(
+            kind="active",
+            name="Active torrents",
+            description="Torrents currently downloading or uploading.",
+            model_cls=QbittorrentWidgetConfig,
+            default_config={},
+            refresh_interval_ms=15_000,
+        ),
+        widget_kind(
+            kind="speed",
+            name="Speed chart",
+            description="Live download/upload speed over a short window.",
+            model_cls=QbittorrentWidgetConfig,
+            default_config={},
+            refresh_interval_ms=5_000,
+        ),
+    ],
+)

backend/src/media_library_viewer_api/integrations/registry.py

@@ -13,6 +13,7 @@ from media_library_viewer_api.integrations.base import ServiceDefinition, Widget
 from media_library_viewer_api.integrations.jellyfin import DEFINITION as JELLYFIN
 from media_library_viewer_api.integrations.nextcloud import DEFINITION as NEXTCLOUD
 from media_library_viewer_api.integrations.prometheus import DEFINITION as PROMETHEUS
+from media_library_viewer_api.integrations.qbittorrent import DEFINITION as QBITTORRENT
 from media_library_viewer_api.integrations.ssh_tasks import DEFINITION as SSH_TASKS
 
 SERVICE_DEFINITIONS: dict[str, ServiceDefinition] = {
@@ -20,6 +21,7 @@ SERVICE_DEFINITIONS: dict[str, ServiceDefinition] = {
     ALERTMANAGER.service_type: ALERTMANAGER,
     JELLYFIN.service_type: JELLYFIN,
     NEXTCLOUD.service_type: NEXTCLOUD,
+    QBITTORRENT.service_type: QBITTORRENT,
     SSH_TASKS.service_type: SSH_TASKS,
     BACKUPS.service_type: BACKUPS,
     AUTHENTIK.service_type: AUTHENTIK,