Add a CalDAV Calendar plugin that syncs tasks with calendar events via
the CalDAV/WebDAV protocol, supporting self-hosted servers like Nextcloud.
Plugin features:
- CalDAV PROPFIND/REPORT for calendar discovery and event fetching
- iCal parsing and serialization with RFC 5545 compliance
- Two-way sync with field mappings (title, notes, dates, duration)
- Time-block integration for auto-creating calendar events
- Multi-calendar support with compound IDs
Host-side changes:
- Add generic request() method to PluginHttp for WebDAV methods
- Add allowPrivateNetwork manifest flag (bundled plugins only)
- Add dynamic loadOptions support for config field dropdowns
- Add backfill effect for existing scheduled tasks
- Generify translation keys (LOAD_OPTIONS instead of LOAD_CALENDARS)
Security:
- SSRF protection via origin validation in resolveHref
- allowPrivateNetwork gated by _isPluginBundled check
- XML parse error detection in CalDAV response parsing
- Description rendered as plain text (not markdown)
Correctness:
- TZID conversion uses formatToParts (no local timezone contamination)
- modifyICalEvent scoped to VEVENT block (preserves VTIMEZONE)
- responseType: 'text' on all CalDAV PUT/DELETE calls
- CR characters handled in iCal text escaping
- Trailing CRLF added to modifyICalEvent output per RFC 5545
