* feat(channels): add automatic link understanding for inbound messages
Auto-detects URLs in inbound messages, fetches content, extracts
title+summary, and enriches the message before the agent sees it.
Includes SSRF protection (rejects private IPs).
* fix(channels): use lowercased string for title extraction to prevent byte offset mismatch
extract_title used byte offsets from the lowercased HTML to index into
the original HTML. Multi-byte characters whose lowercase form has a
different byte length (e.g. İ → i̇) would produce wrong slices or panics.
Fix: extract from the lowercased string directly. Add multibyte test.
65f856d710