feat(safety): report, block and hide chat lines (MODULE_API 1.21.0)

USER_SAFETY.md step 3, the module half of report, block and hide.

- server/safety.js registers the rust.chat report target (snapshot for one
  reader, null when they could not have seen the line; staff's hide and
  unhide) and the steam game identity (ownersOf from rust_account_links).
- The events feed filters chat per reader, in the query: lines from a
  blocked account's Steam ids, the reader's unlinked Steam-ID blocks and the
  lines they hid. Signed-in readers get canBlock on each chat line (false for
  their own and for staff-linked players). Lines staff hid for everyone are
  left out for everyone but staff, who get them with hidden: true.
- rust_events gains hidden_at and hidden_by (ALTER ... IF NOT EXISTS).
- POST /admin/rust/chat/:id/hide and /unhide (admin, moderator), logged.
- The feed's chat lines get a menu: Report, Hide for me, Block player,
  and for staff Hide for everyone / Show to everyone again.
- coreApi ^1.21.0; ci/core-ref.json pinned to the website#233 merge;
  routes.manifest.json and swagger-fragment.json regenerated.

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": "^1.20.0",
+  "coreApi": "^1.21.0",
   "server": "server/index.js",
   "client": { "entry": "client/dist/entry.js" },
   "schema": "server/db/schema.sql",