Hlavicky X-MS365-* jako obycejne hodnoty, GET /users/{user_id}/calendar

- credentials: sifrovani AES-GCM/HKDF odstraneno, tri hlavicky se berou
  tak, jak jsou; bez hlavicek se pouziji hodnoty z prostredi
- zrusena promenna MS365_CREDENTIAL_ENCODING_SECRET a zavislost cryptography
- novy endpoint GET /users/{user_id}/calendar (objekt kalendare schranky,
  id a name) pro read-only overeni pristupu pres e-mail schranky
- C# ukazka posila hodnoty primo, CredentialEncoder smazan
- README: sekce o hlavickach vcetne PowerShell ukazky, zaznam zmen
- .gitignore: bin/ a obj/, zaverzovane obj/ soubory ukazky odstraneny z gitu

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/routes.py

@@ -119,6 +119,12 @@ async def send_mail(
     response.status_code = status.HTTP_202_ACCEPTED
 
 
+@router.get("/users/{user_id}/calendar")
+async def get_calendar(user_id: str, service: CalendarService = Depends(get_calendar_service)) -> Any:
+    """user_id is a Graph user id or the mailbox address, e.g. servis@firma.cz."""
+    return await service.get_calendar(user_id=user_id)
+
+
 @router.get("/users/{user_id}/calendar/events")
 async def list_events(
     user_id: str,