[Server] Add deck share links and public deck visibility (#7241)

* [Server] Add deck share links and public deck visibility

* Address server review comments for deck share links

* Document transaction teardown in deck share rollback paths

* Address second round of deck share review comments

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

servatrice/migrations/servatrice_0036_to_0037.sql

@@ -0,0 +1,71 @@
+-- Servatrice db migration from version 36 to version 37
+
+-- Deck sharing (temporary share links + permanent public decks).
+--
+-- This feature was developed behind several intermediate migrations that have
+-- never shipped, so they are folded into this single 36 -> 37 migration:
+-- temporary share links, permanent public-deck visibility, preview metadata,
+-- and per-deck tags.
+
+-- 1. Temporary deck shares: a named bundle of decks that can be fetched by
+-- anyone who knows the (unguessable) token, until the share expires.
+CREATE TABLE IF NOT EXISTS `cockatrice_deck_share` (
+  `id` int(7) unsigned zerofill NOT NULL auto_increment,
+  `token` varchar(64) COLLATE utf8mb4_bin NOT NULL,
+  `name` varchar(64) NOT NULL,
+  `created_by` int(7) unsigned NULL,
+  `created_at` datetime NOT NULL,
+  `expires_at` datetime NOT NULL,
+  PRIMARY KEY  (`id`),
+  UNIQUE KEY `token` (`token`),
+  KEY `expires_at` (`expires_at`),
+  FOREIGN KEY(`created_by`) REFERENCES `cockatrice_users`(`id`) ON DELETE SET NULL ON UPDATE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci;
+
+-- Individual decks inside a share bundle. Content is materialized at share
+-- time so expiring/deleting a share can cascade cleanly. The metadata columns
+-- are nullable because Qt's MySQL driver binds empty QStrings as NULL when
+-- using prepared statements.
+CREATE TABLE IF NOT EXISTS `cockatrice_deck_share_item` (
+  `id` int(7) unsigned zerofill NOT NULL auto_increment,
+  `share_id` int(7) unsigned zerofill NOT NULL,
+  `name` varchar(50) NOT NULL,
+  `tags` text NULL,
+  `banner_card` varchar(255) NULL,
+  `game_format` varchar(50) NULL,
+  `color_identity` varchar(5) NULL,
+  `content` text NOT NULL,
+  `position` int(7) NOT NULL,
+  PRIMARY KEY  (`id`),
+  KEY `share_id` (`share_id`),
+  FOREIGN KEY(`share_id`) REFERENCES `cockatrice_deck_share`(`id`) ON DELETE CASCADE ON UPDATE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci;
+
+-- 2. Permanent deck sharing: add public visibility flags to the deck storage
+-- tables. A deck is visible to other users if it is marked public, or if any
+-- ancestor folder is marked public (inherited). Existing decks default to
+-- private, so the upgrade does not expose any data.
+ALTER TABLE `cockatrice_decklist_files`
+  ADD COLUMN `is_public` tinyint(1) NOT NULL DEFAULT 0 AFTER `content`;
+
+ALTER TABLE `cockatrice_decklist_folders`
+  ADD COLUMN `is_public` tinyint(1) NOT NULL DEFAULT 0 AFTER `name`;
+
+-- 3. Per-deck preview metadata so clients can render another user's public
+-- decks (e.g. in a visual deck storage grid) without downloading each deck
+-- list. The metadata is derived by the server from the deck content (the color
+-- identity is supplied by the uploading client); decks uploaded before this
+-- migration have empty values until they are re-uploaded.
+ALTER TABLE `cockatrice_decklist_files`
+  ADD COLUMN `banner_card_name` varchar(255) NULL AFTER `is_public`,
+  ADD COLUMN `banner_card_provider` varchar(32) NULL AFTER `banner_card_name`,
+  ADD COLUMN `color_identity` varchar(5) NULL AFTER `banner_card_provider`;
+
+-- 4. Per-deck tags for public decks. The server renders the deck's own tags
+-- into a JSON array, so another user's public decks can filter by tag without
+-- downloading each deck list. Decks uploaded before this migration have NULL
+-- tags until they are re-uploaded.
+ALTER TABLE `cockatrice_decklist_files`
+  ADD COLUMN `tags` text NULL AFTER `color_identity`;
+
+UPDATE cockatrice_schema_version SET version=37 WHERE version=36;