fix(frontend): align NextAuth authorize() with flat backend LoginResponse

Login reached the backend (HTTP 200) but NextAuth returned CredentialsSignin.
Cause: authorize() read data.member.id/email/clubName/clubId, but the backend
LoginResponse is flat — { accessToken, refreshToken, expiresIn, role } with no
member object. Accessing data.member.id on undefined threw, so authorize()
returned null.

Decode the JWT payload to recover identity claims (sub=userId, email,
tenant_id=clubId) and use the flat top-level role. Adds a small decodeJwtPayload
helper (claims only, no signature verification needed here).

cannamanage-frontend/src/lib/auth.ts

@@ -2,6 +2,20 @@ import NextAuth from "next-auth"
 
 import Credentials from "next-auth/providers/credentials"
 
+/**
+ * Decode a JWT payload (no signature verification — we only need the claims for
+ * populating the session). Returns {} on any parse failure.
+ */
+function decodeJwtPayload(token: string): Record<string, unknown> {
+  try {
+    const payload = token.split(".")[1]
+    const json = Buffer.from(payload, "base64url").toString("utf8")
+    return JSON.parse(json) as Record<string, unknown>
+  } catch {
+    return {}
+  }
+}
+
 /** Helper: fetch with an AbortController timeout (default 5s) */
 async function fetchWithTimeout(
   url: string,
@@ -42,14 +56,17 @@ export const { handlers, signIn, signOut, auth } = NextAuth({
 
           if (!res.ok) return null
 
+          // Backend LoginResponse is flat: { accessToken, refreshToken, expiresIn, role }.
+          // Identity claims (sub=userId, email, tenant_id=clubId) live inside the JWT.
           const data = await res.json()
+          const claims = decodeJwtPayload(data.accessToken)
 
           return {
-            id: data.member.id,
+            id: (claims.sub as string) ?? data.accessToken,
-            email: data.member.email,
+            email: (claims.email as string) ?? credentials.email,
-            name: data.member.clubName,
+            name: (claims.email as string) ?? credentials.email,
-            role: data.member.role,
+            role: data.role ?? (claims.role as string),
-            clubId: data.member.clubId,
+            clubId: (claims.tenant_id as string) ?? "",
             accessToken: data.accessToken,
             refreshToken: data.refreshToken,
             expiresAt: Date.now() + data.expiresIn * 1000,