feat: Add torrent favorites/collection management

[Copilot]

Implements a full torrent bookmarks system: users can organize torrents into named collections, manage those collections, and bookmark torrents from search results or PT site pages.

Data Model

• ICollectionFolder — folder metadata (id, name, color, sortIndex, isDefault, torrentIds[])
• TTorrentCollectionKey — composite site:id string for global torrent uniqueness
• Folder metadata lives in IMetadataPiniaStorageSchema.collections; full torrent objects in a separate collectionTorrents key in IExtensionStorageSchema (avoids bloating pinia state with large torrent payloads)
• A default non-deletable collection always exists (DEFAULT_COLLECTION_ID = "default")

export function buildTorrentCollectionKey(torrent: Pick<ITorrent, "site" | "id">): TTorrentCollectionKey {
  return `${torrent.site}:${torrent.id}`;
}

Metadata Store

New getters: isTorrentCollected, getSortedCollections, getCustomCollections, getTorrentCollectionIds

New actions:

• addCollection / editCollection / removeCollection — removing a folder does not delete its torrents
• addTorrentToCollections / addTorrentsToCollections (batch, single IO) / updateTorrentCollections / removeTorrentFromAllCollections — removing a torrent purges it from all folders and extStorage

UI Changes

/my-collection Page (Overview)

• Left panel: folder list with add/edit/delete; default folder is non-deletable
• Right panel: torrent table per selected folder with filter, multi-select, and remove

Bookmark Button Logic (shared)

• No custom collections → direct add/remove from default collection
• Custom collections exist → opens CollectionAddDialog showing a checklist pre-populated with the torrent's current folders

Integration Points

• ActionTd.vue (SearchEntity) — bookmark button appears on single-torrent rows
• SiteDetailPage.vue (content-script) — bookmark SpeedDial button for the detail page torrent
• SiteListPage.vue (content-script) — batch bookmark button for all parsed torrents on the page; uses addTorrentsToCollections to avoid per-torrent storage round-trips

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