feat: improve Quarto snippets

[mcanouil]

• Fix a missing comma in the horizontal rule prefix array that had rendered the file invalid JSON.
• Fix the raw code block syntax so Pandoc raw attributes use the required = prefix ({=html} rather than {html}).
• Fix htm to html in the fenced code block language dropdown, drop the non-standard console, normalise c++/c# to cpp/csharp, and add bash, html, r, rust, sql, toml, typescript, xml, and yaml.
• Add typst to the raw code block dropdown.
• Restore the .column content lines and add tab stops to columns2 and columns3, drop the trailing <!-- end columns --> marker, and append a final $0 so the cursor exits the block cleanly.
• Normalise final cursor placement with $0 on single-line snippets (quote, strikethrough, heading1-heading6).
• Surround block-level snippets (headings, lists, code blocks, divs, blockquote, horizontal rule) with empty lines so the inserted content does not collide with adjacent paragraphs and, for the horizontal rule, cannot be parsed as a setext heading or YAML block delimiter.
• Add yaml for frontmatter, figure for an image with #fig- id and fig-alt, xref for a Quarto cross-reference div (fig-/tbl-/lst-), list-table for a Quarto .list-table div, and tabset for a .panel-tabset block.
• Update the div snippet to use a single placeholder covering id, class, and key-value attributes (::: {#id .class1 key=value}) rather than only a class.