Add player account linking + roster/vendor reads (phase 3)

Ties an in-game account to a website user and gates reads on ownership.

- schema: shard_account_links (account PK → user_id, char_name, linked_at;
  FK users ON DELETE CASCADE) — the site-side mirror of the sidecar's
  authoritative link.
- model/shardLinks: upsert/list/ownership-check/getByAccount/unlink.
- player/shard.controller.js:
  - POST /player/shard/link — confirm a one-time [link code via
    uoLinkClient.confirmLink(code, req.user.id); on link.ok mirror the link and
    activity.log it; bad/expired codes → 400, shard down → 503.
  - GET /player/shard/accounts — the caller's linked accounts.
  - GET /player/shard/roster/:account and /vendors/:account — live round-trips,
    ownership-checked against the mirror (403 otherwise), 503 on shard restart.
- player.routes.js: mounted under the existing requireRole('player') gate with
  express-validator guards + #swagger annotations; new "Player · Shard" tag and
  ShardLinkRequest/ShardLinkResult/ShardLink schemas; spec regenerated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011qPmpmVH1xGCiZoz9m9vW3

server/db/schema.sql

@@ -368,6 +368,21 @@ CREATE TABLE IF NOT EXISTS shard_houses (
   INDEX idx_shard_houses_idoc (is_idoc)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
 
+-- Site-side mirror of in-game-account → website-user links. The sidecar is the
+-- source of truth (it tags the game account with the websiteUserId on
+-- /link/confirm); this table mirrors it so the player portal can list a user's
+-- linked accounts and enforce ownership on roster/vendor reads without a shard
+-- round-trip. account is unique (one game account maps to at most one site user);
+-- a single user may link several game accounts.
+CREATE TABLE IF NOT EXISTS shard_account_links (
+  account    VARCHAR(120) NOT NULL PRIMARY KEY,
+  user_id    INT          NOT NULL,
+  char_name  VARCHAR(120) NULL,
+  linked_at  DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  CONSTRAINT fk_shard_links_user FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
+  INDEX idx_shard_links_user (user_id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
 -- Discord bot moderation core (Phase 2). These tables are owned by the bot
 -- process (its own DB pool, bot/src/db.js) — the main server never reads or
 -- writes them. They live in the same physical database as everything else