feat(admin): metadata-profile picker on integrations page

Persists the operator's metadata-profile choice alongside quality
profile + root folder. Defaults to the first profile Lidarr returns
(usually 'Standard' on a vanilla install) so the common case is
zero-click; operators with custom profiles like 'Singles only' can pick
explicitly.

Backend:
- Migration 0013: adds nullable default_metadata_profile_id to
  lidarr_config. Existing rows get NULL and the service falls back to
  fetch-and-pick-first until they save.
- Updated lidarr_config queries + sqlc + lidarrconfig.Config + admin
  view/put body to round-trip the new field.
- handlePutLidarrConfig requires it (along with QP and root folder)
  when enabled=true — matches the existing missing_defaults gate.
- New GET /api/admin/lidarr/metadata-profiles handler + lidarr.Client
  ListMetadataProfiles (GET /api/v1/metadataprofile, same shape as
  the quality-profile endpoint).
- lidarrrequests.Approve prefers cfg.DefaultMetadataProfileID; falls
  back to the fetch-list path only when 0 (back-compat for upgraders).

Frontend:
- LidarrConfig type + LidarrMetadataProfile type + qk.lidarrMetadataProfiles.
- listMetadataProfiles + createMetadataProfilesQuery client helpers.
- Integrations page: third <select> picker, auto-defaults to first
  profile when the saved value is 0, sends the new field on save and
  clears it on disconnect.
- Updated test fixtures + the duplicate 'Standard' option string in
  the dropdown-populates assertion.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/db/migrations/0013_lidarr_metadata_profile.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE lidarr_config
+    DROP COLUMN default_metadata_profile_id;

internal/db/migrations/0013_lidarr_metadata_profile.up.sql

@@ -0,0 +1,9 @@
+-- M6a follow-up: persist the operator's metadata-profile choice alongside
+-- quality profile + root folder. Lidarr POST /api/v1/artist requires
+-- metadataProfileId; without storing it we'd refetch and pick first on
+-- every Approve, denying the operator a choice. Nullable: existing rows
+-- (and operators upgrading from before this migration) get NULL and the
+-- service falls back to "fetch list and pick first" until they save.
+
+ALTER TABLE lidarr_config
+    ADD COLUMN default_metadata_profile_id integer;