feat(unlinked-books): dismiss (ignore) or delete queue entries

Unidentified sync files used to be stuck: every KOReader re-sync
re-queues them, and there was no way to say "this isn't a book" or "I
don't want this one on the server".

Ignore is the durable dismiss: a new ignored_at column hides the row
from the page list, dashboard badge, and per-device API while the sync
keeps refreshing its metadata (the upsert never clears the column).
A collapsible "Ignored" section lists dismissed rows with Restore and
Delete so a misclick is recoverable. Delete is the hard exit — the row
is gone, and honestly re-queued if the device syncs that file again
(the confirm dialog says so).

Actions are page-scoped SSR routes: htmx swaps in the re-rendered
section so counts and buckets can never drift from the DB; ownership
is row → device → user (admins may act on any row). Integration tests
pin the lifecycle (hide everywhere, survive the sync upsert, restore,
delete), foreign-user 403s, and the render surface.

internal/database/models.go

@@ -562,6 +562,7 @@ type UnlinkedBooks struct {
 	ResolutionMethod pgtype.Text        `db:"resolution_method" json:"resolution_method"`
 	LastSeenAt       pgtype.Timestamptz `db:"last_seen_at" json:"last_seen_at"`
 	CreatedAt        pgtype.Timestamptz `db:"created_at" json:"created_at"`
+	IgnoredAt        pgtype.Timestamptz `db:"ignored_at" json:"ignored_at"`
 }
 
 type UserDashboardPreferences struct {