feat(auth): add signIn rate-limit backfill with dual ip/account budgets

Wires the rate-limit primitive end-to-end through auth.signIn as the
canonical credential-stuffing defence example:

- manifest: rateLimit [ip 5/1m, account 10/1h] on signIn use case
- use case: rateLimit: IRateLimit dep; dual consume + TooManyRequestsError
- binders: ctx.rateLimit ?? new NoopRateLimit() in bind-production + bind-dev-seed
- tRPC: TooManyRequestsError → TOO_MANY_REQUESTS error code in authProcedure
- tests: RecordingRateLimit dual-consume assertion; InMemoryRateLimit
  budget-1 ip + account rejection; coverage 100% on use-cases layer
- ESLint: _manifest-ast.js extractRateLimitNames handles RateLimitBudget
  objects ({name,window,budget}) in addition to plain string literals,
  no-undeclared-rate-limit passes on both "ip" and "account" call sites

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-testing/package.json

@@ -15,6 +15,7 @@
     "./setup/node": "./src/setup/node.ts",
     "./setup/no-instrumentation": "./src/setup/no-instrumentation.ts",
     "./setup/no-sentry": "./src/setup/no-instrumentation.ts",
+    "./rate-limit": "./src/rate-limit/index.ts",
     "./stryker.base.json": "./stryker.base.json"
   },
   "scripts": {