Phase 9c: Parent accounts, magic-link login + parent timetable view

Backend (school-service):
  - parent_account, parent_child, parent_magic_link, parent_session
    tables. Tokens are sha256-hashed in DB; raw goes back exactly
    once to the inviting teacher.
  - InviteParent upserts the parent account, links a child to a tt_
    class, mints a 7-day magic link. Returns the link path so the
    teacher can paste it into Matrix/Email.
  - RedeemMagicLink validates + marks used + mints a 30-day session,
    sets HttpOnly bp_parent_session cookie.
  - ParentSessionMiddleware reads the cookie and resolves the parent.
    Lives in its own router group /api/v1/parent — totally separate
    from the teacher JWT path.
  - ParentMe returns the account + list of children (with class name).
  - ParentTimetable returns the latest completed tt_solution's lessons
    for the requested child's class, with full authorization check
    (parent must own a child in that class).

Frontend (studio-v2):
  - lib/calendar/subject-i18n.ts maps 22 German subject names to 8
    parent locales (de/en/tr/ar/uk/ru/pl/fr). Falls back to German
    for custom subjects.
  - ParentManager component on the Schulkalender page lets the teacher
    invite parents via email + child name + class + language. Newly
    minted magic-link is shown with a copy-to-clipboard button.
  - app/api/parent/[...path]/route.ts proxies parent-side endpoints
    via the cookie so HttpOnly survives the Next.js round-trip.
  - /eltern/login?token=… redeems and redirects to /eltern.
  - /eltern shows a Wochengrid with German days + translated subject
    names in the parent's preferred language. Headings and weekday
    labels also localised (de/en/tr/ar/uk/ru/pl/fr).

Tests:
  - 3 new Go unit tests (random token, hash stability, invite-request
    validator). 83 subtests gesamt.
  - studio-v2: e2e/eltern.spec.ts mit 7 tests across ParentManager,
    /eltern/login, /eltern overview, subject-i18n end-to-end.

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

studio-v2/app/schulkalender/page.tsx

@@ -13,6 +13,7 @@ import { BundeslandWizard } from './_components/BundeslandWizard'
 import { EventModal } from './_components/EventModal'
 import { DayDetail } from './_components/DayDetail'
 import { RolloverWizard } from './_components/RolloverWizard'
+import { ParentManager } from './_components/ParentManager'
 
 function monthRange(year: number, month: number): { from: string; to: string } {
   // Render the visible 6-week grid worth of holidays (covers prev/next month edges).
@@ -168,6 +169,10 @@ export default function SchulkalenderPage() {
                   onDone={() => { setShowRollover(false); loadHolidays() }}
                 />
               )}
+
+              <div className="mt-6">
+                <ParentManager />
+              </div>
             </>
           )}
         </div>