Sync opam package metadata including x-maintenance-intent
and external dependency specifications.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

- Add --dry-run / -n flag to show commands without executing
- Refactor sync steps to accept dry_run parameter
- Show command details in dry-run mode for each step
- Use Eio.Path.mkdirs for recursive directory creation
- Integrate srcsetter as a library for direct invocation
- Fix sortal sync to skip PNG conversion when PNG exists

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

- Add README files for jsonwt, owntracks, monopam, and srcsetter
- Fix langdetect language count (47→49) in dune-project
- Remove unused variable in crockford encode function
- Improve retention type documentation in zulip channels.mli
- Refactor conpool is_healthy to reduce nesting and improve clarity
- Document unimplemented IDNA features in punycode README

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>