Adds GitHub-flavored markdown rendering to message bodies in both
MailboxView and MailboxModal via a shared MailboxMessageContent
component (ReactMarkdown + remark-gfm). Plain-text messages render
unchanged. Raw HTML is not executed.
- New MailboxMessageContent component with mailbox-scoped pre/table/link
overrides; links open in a new tab with noopener noreferrer.
- Wired into the full message body and conversation thread bodies in
both Mailbox surfaces (parity preserved).
- CSS for .mailbox-markdown, .mailbox-markdown-pre, .mailbox-markdown-table
with horizontal scroll for code blocks/tables; removed white-space:
pre-wrap on bodies since markdown owns its own whitespace.
- 10 new unit tests cover headings, lists, bold/italic, inline code,
fenced code blocks, link target/rel, GFM tables, plain-text passthrough,
raw-HTML safety, and testId forwarding. Existing 108 mailbox tests
continue to pass.
