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/db/queries/search.sql

@@ -9,6 +9,9 @@ UPDATE acquisition_settings
        search_interval_hours = sqlc.arg(search_interval_hours),
        allowed_qualities     = sqlc.arg(allowed_qualities),
        import_root           = sqlc.arg(import_root),
+       seed_ratio            = sqlc.arg(seed_ratio),
+       seed_days             = sqlc.arg(seed_days),
+       stall_hours           = sqlc.arg(stall_hours),
        updated_at            = now()
  WHERE id = true
 RETURNING *;
@@ -109,14 +112,23 @@ UPDATE grabs
  WHERE id = sqlc.arg(id) AND ended_at IS NULL;
 
 -- name: ListReleaseBlocks :many
-SELECT * FROM release_blocks ORDER BY blocked_at DESC;
+-- Every release set aside and still held back: a stalled one lifts by itself
+-- at expires_at (#5523).
+SELECT * FROM release_blocks
+ WHERE expires_at IS NULL OR expires_at > now()
+ ORDER BY blocked_at DESC;
 
 -- name: BlockRelease :exec
-INSERT INTO release_blocks (info_hash, name, reason, detail, want_id, blocked_by)
+-- A release set aside. expires_at NULL is for good. A block for good is never
+-- shortened by a timed one: only a timed block, or another for good, is
+-- replaced.
+INSERT INTO release_blocks (info_hash, name, reason, detail, want_id, blocked_by, expires_at)
 VALUES (sqlc.arg(info_hash), sqlc.arg(name), sqlc.arg(reason), sqlc.arg(detail),
-        sqlc.narg(want_id), sqlc.narg(blocked_by))
+        sqlc.narg(want_id), sqlc.narg(blocked_by), sqlc.narg(expires_at))
 ON CONFLICT (info_hash) DO UPDATE
-   SET reason = EXCLUDED.reason, detail = EXCLUDED.detail, blocked_at = now();
+   SET reason = EXCLUDED.reason, detail = EXCLUDED.detail, blocked_at = now(),
+       expires_at = EXCLUDED.expires_at, blocked_by = EXCLUDED.blocked_by
+ WHERE release_blocks.expires_at IS NOT NULL OR EXCLUDED.expires_at IS NULL;
 
 -- name: UnblockRelease :execrows
 DELETE FROM release_blocks WHERE info_hash = $1;