feat: download lifecycle — stalled and failed downloads are given up and searched again; imported ones seed, then go (M502 #5523)

Ported from Fabled Librarian's System 104. A new lifecycle poller, every
ten minutes:
- a download the client fails is given up at once;
- one nobody shares, or still fetching its file list, past the stall
  setting (6 h) is asked for again three times, then given up;
- giving up removes the download with its files, holds the release back
  for a week (release_blocks.expires_at), ends the grab and searches the
  album again, with no limit per album;
- a running download the client stops listing for half an hour ends and is
  searched again, not held back; an empty list is not taken as gone;
- an imported download seeds to ratio 2.0 or 14 days, then is removed;
- a download the client would not remove is asked again every pass.

Every condition and act is one open row per (client, download, condition)
in download_interventions. Activity shows what is wrong with a download and
how often it was retried, why one ended, its seeding, and a banner for a
client that does not answer. A running download can be given up by hand
(set aside for good). The seed ratio, seed days and stall hours are on the
search settings card. The download client lookup moves to
acquire.DownloadClientFor, shared by the importer and the lifecycle.

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

internal/api/admin_search.go

@@ -37,6 +37,12 @@ type searchSettingsView struct {
 	// is the first of ScanPaths, the library's folders.
 	ImportRoot string   `json:"import_root"`
 	ScanPaths  []string `json:"scan_paths"`
+	// The download lifecycle (#5523): seed an imported download to this
+	// ratio or for this many days; give up on one nobody shares after this
+	// many hours. 0 is: remove once imported, no time limit, never.
+	SeedRatio  float32 `json:"seed_ratio"`
+	SeedDays   int32   `json:"seed_days"`
+	StallHours int32   `json:"stall_hours"`
 }
 
 func searchSettings(s dbq.AcquisitionSetting, roots []string) searchSettingsView {
@@ -44,6 +50,7 @@ func searchSettings(s dbq.AcquisitionSetting, roots []string) searchSettingsView
 		AutoGrab: s.AutoGrab, SearchIntervalHours: s.SearchIntervalHours,
 		AllowedQualities: s.AllowedQualities, Tiers: release.Tiers, LastPass: s.LastPass,
 		ImportRoot: s.ImportRoot, ScanPaths: roots,
+		SeedRatio: s.SeedRatio, SeedDays: s.SeedDays, StallHours: s.StallHours,
 	}
 	if v.ScanPaths == nil {
 		v.ScanPaths = []string{}
@@ -76,6 +83,9 @@ type putSearchSettingsBody struct {
 	SearchIntervalHours int32    `json:"search_interval_hours"`
 	AllowedQualities    []string `json:"allowed_qualities"`
 	ImportRoot          string   `json:"import_root"`
+	SeedRatio           float32  `json:"seed_ratio"`
+	SeedDays            int32    `json:"seed_days"`
+	StallHours          int32    `json:"stall_hours"`
 }
 
 // handlePutSearchSettings implements PUT /api/admin/acquisition/settings.
@@ -102,9 +112,15 @@ func (h *handlers) handlePutSearchSettings(w http.ResponseWriter, r *http.Reques
 		writeErr(w, apierror.BadRequest("bad_import_root", "file new music into one of the library's folders"))
 		return
 	}
+	if body.SeedRatio < 0 || body.SeedRatio > 100 || body.SeedDays < 0 || body.SeedDays > 365 ||
+		body.StallHours < 0 || body.StallHours > 720 {
+		writeErr(w, apierror.BadRequest("bad_lifecycle",
+			"seed ratio must be 0 to 100, seed days 0 to 365 and stall hours 0 to 720"))
+		return
+	}
 	s, err := dbq.New(h.pool).UpdateAcquisitionSettings(r.Context(), dbq.UpdateAcquisitionSettingsParams{
 		AutoGrab: body.AutoGrab, SearchIntervalHours: body.SearchIntervalHours, AllowedQualities: body.AllowedQualities,
-		ImportRoot: body.ImportRoot,
+		ImportRoot: body.ImportRoot, SeedRatio: body.SeedRatio, SeedDays: body.SeedDays, StallHours: body.StallHours,
 	})
 	if err != nil {
 		writeErrWithLog(w, h.logger, "admin search settings: put", apierror.Internal(err))