feat(rust): identity — a link code from the game, and the Steam id inside core's user page

R1's identity link, site-side, and R13's first extension slot. A player types
/link in game, the plugin hands them a six-character code privately, and they
enter it here; the site records who owns which Steam account, and an operator
sees that on core's own `/admin/users/:id` page.

**The site is the author of record and the game holds nothing.** There is no
per-account store in Rust that survives a wipe, and phase 7 needs the site
authoritative anyway — it pushes permissions INTO the game keyed by Steam id. A
copy in the game would be a second thing to reconcile every wipe, for no question
it could answer better.

## D24 — a code is minted by ONE server, so every server is asked

Nothing in six characters says where it came from. The fleet is asked in turn and
the first `link.ok` wins; the others answer `unknown` and nothing happens there,
because a code is only spent at the server that actually holds it. Asking the
player to pick was rejected: a wrong pick would come back indistinguishable from
a wrong code, and that is the one refusal which must not be ambiguous.

**"Every reachable server refused" is not the same answer as "a server was
unreachable."** Collapsing them tells a player whose server is down that their
code is wrong — so they run /link again on that same server and are told the same
thing for as long as it stays down. `unsure` is that case, and it says to try
again rather than to fetch a new code.

## D23 — a Steam id another account holds is refused, never moved

The primary key is `steam_id`, and it is load-bearing rather than tidy: phase 7
grants permissions against a link and phase 13 hangs entitlements off it, so a
silent move is an account takeover performed by typing six characters. The
refusal names the holder, because the advice is unusable without it. The INSERT
is a plain INSERT for the same reason — `ON DUPLICATE KEY UPDATE` here would BE
that move — and the duplicate-key error is the refusal for the race the check
above cannot close.

The way out is `/unlink` in game, which reaches the site off the ingest feed
rather than through a route (the plugin has no link to delete). D25 adds the
other way out: staff can sever a link from the admin panel, for a player who
cannot reach that Steam account in game.

## The slot, and the hole it found in this repo's own generator

`admin.users.detail` is declared in `module.json` AND registered in `index.js`
AND filled by the chunk — three places, because the server half and the client
half are different registrations that share one name.

`swaggerFragment.js` knew only about tier routers, so the two routes under
`/admin/users/:id` were generated by nothing: a fragment that was internally
consistent and described two routes fewer than the module serves. A slot's mount
is core's and cannot be derived here, so it is a fourth constant beside
`TIER_BASE` — held to account by the frozen-manifest job, which was verified to
catch exactly this by removing the two paths and watching it fail.

## Smaller things worth knowing

- **Core's `useAsync` has no `refresh`.** A counter in the deps is how a page
  re-reads after its own write; it blanks while it re-reads, which is right here
  and is exactly what made it wrong for a poll.
- **Every player-portal nav row needs an `icon`** — core draws one on every row,
  and the client suite says so. This module had no icons file until now, because
  the public header is text buttons.
- The two new frame kinds are STAFF-only. Neither carries a code, but both name a
  Steam id beside a website account's activity, and that join is not a public
  fact about what happened on a server.
- The link code route carries its own rate limiter rather than core's
  `accountChangeLimiter`: this is guessing somebody else's secret, not changing
  your own password, and a shared counter would let one policy set the other.

Protocol 3 on all three declaration sites; 17 new tests, 136 green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMH6bw1jXMgbyF3ZWGEzSM

server/db/schema.sql

@@ -291,6 +291,50 @@ CREATE TABLE IF NOT EXISTS rust_ingest_cursor (
 );
 
 
+-- ── Who owns which Steam account ──────────────────────────────────────────
+--
+-- R1's identity link, and the reason it is a table rather than a column on
+-- `rust_players`: a link is a fact about a WEBSITE USER that happens to be keyed
+-- by a Steam id, and it outlives every row this module writes about play. A
+-- column here would be null for the overwhelming majority of players and would
+-- be deleted by any sweep that pruned inactive ones.
+--
+-- **Keyed on `steam_id` alone, fleet-wide.** `rust_players` already made that
+-- call in protocol 2 and it is the truth of the thing: a Steam account is one
+-- person across every server an operator runs, where stats are per server and
+-- per wipe. Linking on one server links for the fleet, because there is nothing
+-- else it could honestly mean.
+--
+-- **One Steam id, at most one user** — that is what the primary key buys, and it
+-- is load-bearing rather than tidy. Phase 7 makes the site the author of who may
+-- do what in game and phase 13 makes it the thing that hands out loot; both are
+-- grants against a Steam id, and both assume the question "whose is this?" has
+-- exactly one answer.
+--
+-- The reverse is deliberately NOT constrained: one website user may hold several
+-- Steam accounts. People have a second account, or a family shares a site login,
+-- and refusing that would be inventing a rule the game does not have.
+--
+-- `ON DELETE CASCADE` from `users`: a deleted account's links go with it. The
+-- alternative is a row naming a user id that resolves to nobody, which every
+-- read would then have to defend against.
+CREATE TABLE IF NOT EXISTS rust_account_links (
+  steam_id   VARCHAR(32)  NOT NULL PRIMARY KEY,
+  user_id    INT          NOT NULL,
+  -- What the player was called in game when they linked. A display name, kept
+  -- so an operator reading the admin panel sees a person rather than a number;
+  -- never used to identify anybody, because a Rust name changes on a whim.
+  name       VARCHAR(191) NULL,
+  -- Which server minted the code. Not part of the identity — the link is
+  -- fleet-wide — but an operator asking "where did this come from" has no other
+  -- way to find out, and a support conversation starts there.
+  server_id  VARCHAR(64)  NULL,
+  linked_at  DATETIME     NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  CONSTRAINT fk_rust_links_user FOREIGN KEY (user_id) REFERENCES users (id) ON DELETE CASCADE,
+  KEY idx_rust_links_user (user_id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+
 -- ── Changes to tables that already shipped ────────────────────────────────
 --
 -- An ALTER below the CREATE, never an edit to it: `CREATE TABLE IF NOT EXISTS`