feat(cardav): add Migration 30 for CardDAV contacts schema

Add comprehensive database schema for CardDAV multi-account contacts sync:

New tables:
- cardav_accounts: Store CardDAV server credentials
- cardav_addressbook_selection: Per-account addressbook enable/disable
- contact_phones: Multiple phone numbers per contact with labels
- contact_emails: Multiple email addresses per contact with labels
- contact_addresses: Multiple postal addresses per contact with labels

Extended contacts table with 9 new columns:
- organization, job_title, birthday, website, photo, nickname
- cardav_account_id (FK to cardav_accounts, ON DELETE SET NULL)
- cardav_uid (vCard UID from server)
- cardav_addressbook_url (source addressbook URL)

Features:
- UNIQUE constraints on (cardav_url, username) and (account_id, addressbook_url)
- CASCADE delete for addressbook selection and contact sub-tables
- Performance indices for cardav_uid and email lookups
- Support for manual contacts (NULL cardav_account_id)
- is_primary flag for phone/email/address selection

Test coverage:
- 23 comprehensive tests verify all tables, constraints, indices
- FK CASCADE delete behavior validated
- UNIQUE constraints enforced
- Data integrity scenarios tested

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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