refactor(#411): QA-011 — unify request-with-user types into AuthenticatedRequest

Replace 4 redundant request interfaces (RequestWithSession, AuthRequest,
BetterAuthRequest, RequestWithUser) with AuthenticatedRequest and
MaybeAuthenticatedRequest in apps/api/src/auth/types/.

- AuthenticatedRequest: extends Express Request with non-optional user/session
  (used in controllers behind AuthGuard)
- MaybeAuthenticatedRequest: extends Express Request with optional user/session
  (used in AuthGuard and CurrentUser decorator before auth is confirmed)
- Removed dead-code null checks in getSession (AuthGuard guarantees presence)
- Fixed cookies type safety in AuthGuard (cast from any to Record)
- Updated test expectations to match new type contract

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

apps/api/src/auth/decorators/current-user.decorator.ts

@@ -1,14 +1,13 @@
 import type { ExecutionContext } from "@nestjs/common";
 import { createParamDecorator, UnauthorizedException } from "@nestjs/common";
 import type { AuthUser } from "@mosaic/shared";
-
-interface RequestWithUser {
-  user?: AuthUser;
-}
+import type { MaybeAuthenticatedRequest } from "../types/better-auth-request.interface";
 
 export const CurrentUser = createParamDecorator(
   (_data: unknown, ctx: ExecutionContext): AuthUser => {
-    const request = ctx.switchToHttp().getRequest<RequestWithUser>();
+    // Use MaybeAuthenticatedRequest because the decorator doesn't know
+    // whether AuthGuard ran — the null check provides defense-in-depth.
+    const request = ctx.switchToHttp().getRequest<MaybeAuthenticatedRequest>();
     if (!request.user) {
       throw new UnauthorizedException("No authenticated user found on request");
     }