feat(rust): a Steam account linked on the site is a Rust link (D392, D396)

Registers core's MODULE_API 1.17.0 identity hooks (coreApi ^1.17.0):
onIdentityLinking refuses a Steam id that is another website account's Rust
link (D396); onIdentityLinked writes the Rust link with the PRIMARY KEY as the
race guard, reconciles Teams and raises the linked notice, as /link does.
Unlinking Steam leaves the Rust link (D393); the Rust account page says so.

ci/core-ref.json still pins the 1.15.0 core and must move to the website
branch head carrying 1.17.0 before CI can pass.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

module.json

@@ -2,7 +2,7 @@
   "id": "rust",
   "name": "Rust",
   "version": "0.1.0",
-  "coreApi": "^1.15.0",
+  "coreApi": "^1.17.0",
   "server": "server/index.js",
   "client": { "entry": "client/dist/entry.js" },
   "schema": "server/db/schema.sql",