Panel and hover: style the code in message notes and link their lines #192

Follow-up to the structured message notes in the verifier (liquid-java/liquidjava#532). In the Verification panel and in the hover:

• show the code segments of a note (for example new BufferedInputStream(stream) and markState(buffered) == unmarked in Origin: line 134, …) in the editor font, set apart from the prose;
• make source references such as line 134 clickable, jumping to that line.

VS Code shows a diagnostic's message as plain text: no markdown in the Problems tab or the diagnostic hover. So the panel, which is HTML, gets full styling and links. In the hover, either keep plain text or add an extension HoverProvider with a MarkdownString (code spans and command links). Check which reads better at the study's width and doesn't duplicate the diagnostic hover.