feat(auth): admin access link doubles as magic-login for users with passwords

The original generateAccessLink branched on user state and minted either
an invite URL (forces password setup) or a reset URL (forces password
change). Both required the user to set/change a password — fine for new
users, painful for tech-illiterate sponsor jurors who already have a
working password and just need a fresh login because their JWT went
stale or their email is bouncing.

This adapts the existing invite-token flow to behave as a magic-login
when the user already has a password:

  - auth.ts credentials.authorize: only set mustSetPassword=true if the
    user has no passwordHash. Users who already set one keep it, the
    invite token is consumed, JWT is issued with their current role,
    they're signed in.
  - accept-invite/page.tsx: redirect to / after accept (was hardcoded
    to /set-password). The middleware already enforces the
    /set-password detour when mustSetPassword is true, so users who
    need it still land there; everyone else routes by role.
  - generateAccessLink: drop the reset-password branch. Always emits an
    /accept-invite URL. The flow naturally adapts: setup for new users,
    magic-login for active ones. Audit log records which behavior fired
    (kind: 'setup' | 'magic_login').
  - dialog copy: clearer description for each kind.

Net behavior: Didier (active, has password, stale JWT after role
migration) clicks his link → instant login on /jury, password preserved.
Magali (no password yet) clicks hers → /set-password → onboarding.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/(admin)/admin/members/[id]/page.tsx

@@ -128,7 +128,7 @@ export default function MemberDetailPage() {
   const [accessLinkOpen, setAccessLinkOpen] = useState(false)
   const [accessLink, setAccessLink] = useState<{
     url: string
-    kind: 'invite' | 'reset'
+    kind: 'setup' | 'magic_login'
     expiresAt: Date
   } | null>(null)
   const [linkCopied, setLinkCopied] = useState(false)
@@ -918,9 +918,9 @@ export default function MemberDetailPage() {
               Access link ready
             </DialogTitle>
             <DialogDescription>
-              {accessLink?.kind === 'invite'
-                ? `Share this with ${user.name || user.email} via Slack, WhatsApp, or any channel that reaches them. They'll be walked through accepting the invite, setting a password, and onboarding.`
-                : `Share this with ${user.name || user.email} so they can pick a new password. They'll land on their dashboard once done.`}
+              {accessLink?.kind === 'magic_login'
+                ? `Share this with ${user.name || user.email} via Slack, WhatsApp, or any channel that reaches them. Clicking it will sign them in directly (their existing password is preserved) and take them to their dashboard.`
+                : `Share this with ${user.name || user.email} via Slack, WhatsApp, or any channel that reaches them. They'll be walked through setting a password and onboarding.`}
             </DialogDescription>
           </DialogHeader>