feat: account linking for magic link + Google, last login method hint

- Move account linking config out of Google conditional so it's always active
- Trust both 'google' and 'email' providers for automatic account linking
- Add lastLoginMethod plugin to track how users last signed in
- Show "Last signed in with Google/email link" hint in sign-in dialog

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/auth/src/client.ts

@@ -1,4 +1,4 @@
-import { magicLinkClient } from 'better-auth/client/plugins'
+import { lastLoginMethodClient, magicLinkClient } from 'better-auth/client/plugins'
 import { createAuthClient } from 'better-auth/react'
 
 /**
@@ -45,7 +45,7 @@ function getAuthURL(): string {
  */
 export const authClient = createAuthClient({
   baseURL: getAuthURL(),
-  plugins: [magicLinkClient()],
+  plugins: [magicLinkClient(), lastLoginMethodClient()],
 })
 
 /**

packages/auth/src/server.ts

@@ -3,7 +3,7 @@ import { schema } from '@pascal-app/db'
 import type { BetterAuthOptions } from 'better-auth'
 import { betterAuth } from 'better-auth'
 import { drizzleAdapter } from 'better-auth/adapters/drizzle'
-import { magicLink } from 'better-auth/plugins'
+import { lastLoginMethod, magicLink } from 'better-auth/plugins'
 
 export interface SendMagicLinkParams {
   email: string
@@ -61,6 +61,13 @@ export function createAuth(config: AuthConfig): ReturnType<typeof betterAuth> {
         },
       },
     },
+    // Account linking — always enabled so magic link + Google users can share accounts
+    account: {
+      accountLinking: {
+        enabled: true,
+        trustedProviders: ['google', 'email'],
+      },
+    },
     // Google OAuth provider (only enabled when credentials are provided)
     ...(config.googleClientId &&
       config.googleClientSecret && {
@@ -70,15 +77,11 @@ export function createAuth(config: AuthConfig): ReturnType<typeof betterAuth> {
             clientSecret: config.googleClientSecret,
           },
         },
-        account: {
-          accountLinking: {
-            enabled: true,
-            trustedProviders: ['google'],
-          },
-        },
       }),
     plugins: [
       ...(config.additionalPlugins ?? []),
+      // Track which login method was last used (e.g., "google", "magic-link")
+      lastLoginMethod(),
       // Magic link authentication
       ...(config.sendMagicLink
         ? [