refactor: add shared utilities and replace console.log with logger

- Add shared action-utils.ts with getCurrentUserId and requireAuth helpers
- Add shared constants for anki defaults (FIELD_SEPARATOR, DEFAULT_NEW_PER_DAY, DEFAULT_REV_PER_DAY)
- Add shared time constants (SECONDS_PER_DAY, MS_PER_DAY, etc.)
- Replace console.error with logger in auth.ts

src/auth.ts

@@ -4,6 +4,10 @@ import { nextCookies } from "better-auth/next-js";
 import { username } from "better-auth/plugins";
 import { createAuthMiddleware, APIError } from "better-auth/api";
 import { prisma } from "./lib/db";
+import { createLogger } from "./lib/logger";
+
+const log = createLogger("auth");
+
 import {
   sendEmail,
   generateVerificationEmailHtml,
@@ -24,7 +28,7 @@ export const auth = betterAuth({
         html: generateResetPasswordEmailHtml(url, user.name || "用户"),
       });
       if (!result.success) {
-        console.error("[email] Failed to send reset password email:", result.error);
+        log.error("Failed to send reset password email", { error: result.error });
       }
     },
   },
@@ -38,7 +42,7 @@ export const auth = betterAuth({
         html: generateVerificationEmailHtml(url, user.name || "用户"),
       });
       if (!result.success) {
-        console.error("[email] Failed to send verification email:", result.error);
+        log.error("Failed to send verification email", { error: result.error });
       }
     },
   },

src/modules/shared/action-utils.ts

@@ -0,0 +1,25 @@
+"use server-headers";
+
+import { auth } from "@/auth";
+import { headers } from "next/headers";
+import { createLogger } from "@/lib/logger";
+
+const log = createLogger("shared-action-utils");
+
+export async function getCurrentUserId(): Promise<string | null> {
+  const session = await auth.api.getSession({ headers: await headers() });
+  if (!session?.user?.id) {
+    log.warn("Unauthenticated access attempt");
+    return null;
+  }
+  return session.user.id;
+}
+
+export async function requireAuth(): Promise<string> {
+  const userId = await getCurrentUserId();
+  if (!userId) {
+    log.warn("Authentication required but rejected");
+    throw new Error("Unauthorized");
+  }
+  return userId;
+}