feat: indexers and download clients you add and configure (M502 #5518)

Admin → Integrations gains "Indexers and download clients": two lists of
connections the operator adds, Fabled Librarian's model. Nothing is seeded
or copied from Lidarr.

- Indexers: Prowlarr (its native /api/v1/search, which asks every indexer
  at once; Prowlarr has no aggregate Torznab feed) and any Torznab feed.
- Download clients: qBittorrent (WebUI v2, with re-login on an expired
  session) and FabledExchange, one entry with a switch per job:
  downloads (/api/downloads), search (/api/search) and release details
  (/api/torrents/{infohash}). All three start on; its key is optional.
- Each entry: enable, name, address, a write-only key or password, Test.
  A download client's Test lists its torrents and checks the downloads
  folder is visible and writable from Minstrel; an Exchange's Test
  reports each job switched on.
- Download clients carry a path mapping (Minstrel's /downloads vs the
  client's own name for it); search sources carry searches per hour.

Migration 0079 adds acquisition_services with its CHECKs. Ported from
Fabled Librarian: internal/indexer (Torznab, 429 Retry-After, magnet
redirects), internal/prowlarr, internal/exchange, internal/downloader,
and internal/acquire's one builder per kind, which Test already uses
so a passing Test vouches for the path a grab will take.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/dbq/models.go

@@ -195,6 +195,28 @@ type AcoustidSetting struct {
 	UpdatedAt pgtype.Timestamptz
 }
 
+type AcquisitionService struct {
+	Code             string
+	Kind             string
+	Protocol         string
+	Label            string
+	Enabled          bool
+	BaseUrl          string
+	ApiKey           string
+	Username         string
+	Password         string
+	Category         string
+	TimeoutMs        int32
+	ServesSearch     bool
+	ServesDownloads  bool
+	ServesEnrichment bool
+	LocalPath        string
+	RemotePath       string
+	SearchesPerHour  int32
+	CreatedAt        pgtype.Timestamptz
+	UpdatedAt        pgtype.Timestamptz
+}
+
 type Album struct {
 	ID                     pgtype.UUID
 	Title                  string