feat(auth): bind signIn through ProductionUseCase<I, O, M> branded slot

Adds explicit ProductionUseCase<SignInInput, SignInOutput, AuthManifest["useCases"]["signIn"]>
type annotation to wrappedSignIn in bind-production.ts. To satisfy the Instrumented & Captured
intersection requirement, withSpan gains a brand-preserving overload so composing
withSpan ∘ withCapture returns Instrumented<F> & Captured<F>.

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

packages/core-shared/src/instrumentation/with-span.ts

@@ -1,6 +1,16 @@
 import type { ITracer, SpanOpts } from "./tracer.interface";
 import type { Instrumented } from "../conformance/brands";
 
+export function withSpan<Args extends unknown[], R, Extra extends object>(
+  tracer: ITracer,
+  opts: SpanOpts | ((args: Args) => SpanOpts),
+  fn: ((...args: Args) => Promise<R>) & Extra,
+): Instrumented<((...args: Args) => Promise<R>) & Extra>;
+export function withSpan<Args extends unknown[], R>(
+  tracer: ITracer,
+  opts: SpanOpts | ((args: Args) => SpanOpts),
+  fn: (...args: Args) => Promise<R>,
+): Instrumented<(...args: Args) => Promise<R>>;
 export function withSpan<Args extends unknown[], R>(
   tracer: ITracer,
   opts: SpanOpts | ((args: Args) => SpanOpts),