feat(profile): first/last name fields + collapse notification preferences

Two related cleanups for the user profile surface area:

(1) Add canonical first_name + last_name columns to user_profiles.
    Migration 0049 backfills from display_name by splitting on the
    first whitespace run; single-token names land as
    (display_name, NULL) so we never throw away existing data.
    Display name becomes an optional override (nicknames, vanity
    formatting). /api/v1/me PATCH now accepts firstName/lastName,
    and the user-settings form surfaces them as the primary inputs
    with display name as a secondary "How your name appears" field.

(2) Remove the broken Notifications card from user-settings (it called
    PATCH on an endpoint that has GET/PUT only and used a flat shape
    vs the actual array shape). Replace with the working
    NotificationPreferencesForm + ReminderDigestForm under a
    #notifications anchor. /notifications/preferences becomes a
    server-side redirect to /settings#notifications for back-compat;
    the mobile More-sheet + user-menu Bell entry now deep-link to the
    new anchor directly.

Drops the auto-generated drizzle-kit catch-up migration so we're not
sneaking accumulated schema drift into the journal — only the targeted
0049 lands here.

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

src/components/layout/user-menu.tsx

@@ -126,7 +126,7 @@ export function UserMenu({ trigger, align = 'end', user, ports }: UserMenuProps)
         </DropdownMenuItem>
         <DropdownMenuItem
           // eslint-disable-next-line @typescript-eslint/no-explicit-any
-          onClick={() => router.push(`${base}/notifications/preferences` as any)}
+          onClick={() => router.push(`${base}/settings#notifications` as any)}
         >
           <Bell className="w-4 h-4 mr-2" />
           Notification preferences