fix(kms/auth-eth): unblock Slither CI (lockfile + SPDX)

Two CI failures on e54868e:

1. Slither CI failed because the crytic/slither-action runs `npm ci` and
   package-lock.json was out of sync with package.json after the earlier
   dep cleanup (dropped @openzeppelin/contracts-upgradeable, supertest,
   @types/supertest; fastify et al were already drifted). Regenerated by
   running `npm install` locally; `npm ci` now succeeds and `npx jest`
   still passes (4/4).

2. SPDX/REUSE check failed because kms/auth-eth/slither.config.json had
   no copyright header (JSON has no comment syntax). Added it to the
   REUSE.toml annotation list alongside the other auto-generated /
   config-only JSON files.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: h4x3rotab

REUSE.toml

@@ -23,6 +23,7 @@ path = [
     "**/tsconfig.node.json",
     "**/tsconfig.browser.json",
     "kms/auth-eth-bun/.oxlintrc.json",
+    "kms/auth-eth/slither.config.json",
     "package-lock.json",
     "**/package-lock.json",
     "kms/auth-eth/.openzeppelin/unknown-2035.json",