Matrix HTML table helpers and pipe-table Markdown support

[TroyHernandez]

What

mx_table_html() and mx_send_table() render a data frame, matrix, or list as the conservative table HTML Matrix clients accept: a bare <table> of <tr>/<th>/<td>, no CSS, colspan, rowspan, or custom attributes. mx_send_table() pairs it with a plain-text body for clients that ignore formatted_body.

mx_markdown_to_html() gains GitHub-style pipe tables, honouring the :---/:---:/---: alignment row.

Adds inst/skills/mx.client/matrix-messaging/SKILL.md.

Two corrections folded in

NEWS. The table helpers had been written into the # mx.client 0.1.1 section, which already shipped to CRAN. Moved to a new 0.1.1.2 heading so the released notes describe what was actually released.

Dropped example. The markdown.R rewrite expanded mx_pill_mentions' @param/@return prose but lost its @examples block. tinyrox flags it and CRAN wants examples on exported functions, so it's restored.

Note

rformat_dir("R") also reflowed R/messages.R, which this branch never touched. The repo was not rformat-clean. That churn is isolated in its own commit.

Verification

75 tests pass. The restored example runs clean:

mx_pill_mentions("<p>ping @jorge</p>", "@jorge:example.org")
#> "<p>ping <a href=\"https://matrix.to/#/@jorge:example.org\">jorge</a></p>"

[TroyHernandez]

Both findings confirmed and fixed.

header = FALSE fallback. mx_table_html() honoured header, mx_table_plain() always emitted column names, so formatted_body and the plain-text body showed different tables to different clients. mx_table_plain() now takes header and mx_send_table() passes it through.

1) ordered lists. Confirmed regression. main matched ^\\s*[0-9]+[.)]\\s+; the rewrite matched only \\., so 1) input silently rendered as a paragraph. Restored.

There were no ordered-list tests at all, which is how it got through. Added coverage for both markers, plus mx_table_plain() with and without a header.

80 tests, 0 failures (markdown 16 to 18, tables 2 to 5).