medcenterphysio: apply the v3 design and add the callback dialog

v3 differs from legacy/new only by the callback dialog; the new phone
number was already in the React landing.

The header «Звонок» button opens the «Перезвоним вам» dialog from the
fitness landing (name, phone, consent), ported the same way as in
medcenterstart: the phone field keeps this landing's +7 mask and refuses
fewer than 11 digits, as the mockup does. The server accepts form
'callback', names the deal «Обратный звонок — <имя>» and tags it
«обратный звонок». The phone link inside the dialog and the call button
in the mobile action bar still report a call click.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

medcenterphysio/shared/lead.ts

@@ -1,7 +1,7 @@
 import { z } from 'zod'
 
 /** Which form on the page produced the lead. Surfaces as an amoCRM tag. */
-export const leadFormIds = ['request'] as const
+export const leadFormIds = ['request', 'callback'] as const
 export type LeadFormId = (typeof leadFormIds)[number]
 
 export const utmKeys = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_content', 'utm_term'] as const