Merge PR 822: feat: compatibility hints for sync, multiget and DELETE quirks

#822

Compatibility features and server profiles for the sync, multiget,
PROPFIND-limit and DELETE behaviours a sync client depends on, plus
three SOGo rewrites, measured with caldav-server-tester on 22 servers.
The Stalwart test container now runs with WebDav.maxResults 50
(STALWART_MAX_RESULTS), and Infomaniak loses its ungraceful
sync-token.delete hint, made obsolete by PR 821.

Commits:
- 66d2354 feat: hints for three SOGo rewrites
- ecef3a1 feat: features for sync, multiget, DELETE quirks
- 11cdcb2 feat: profile the sync, multiget and DELETE quirks
- 6597b51 docs: two feature descriptions follow the probes

Assisted-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Reviewed-by: Tobias Brox <tobias@redpill-linpro.com>

Author: tobixen