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/auth/src/feature.manifest.ts

@@ -21,6 +21,10 @@ export const authManifest = defineFeature({
       audits: [],
       publishes: [],
       consumes: [],
+      rateLimit: [
+        { name: "ip", window: "1m", budget: 5 },
+        { name: "account", window: "1h", budget: 10 },
+      ],
     },
     signUp: {
       mutates: true,