[DSGVO] 2. Auskunft & Datenübertragbarkeit — Art. 15, Art. 20

[thomiel]

No way to answer a member's access request except manual DB spelunking.
Add one "member data report" function collecting everything tied to a member
(C3sMember row, Shares, Dues/invoices, general assembly invitations)
rendered (a) as PDF for Art. 15 including the mandatory metadata (purposes,
recipients, storage duration, rights, supervisory authority) and (b) as
JSON/CSV for Art. 20. The email_confirm_token self-service pattern used
for certificates would let members request this themselves.