feat: clickable URLs in chat log

Adds a parsing step when constructing `Message` objects that scans the
message content for anything that looks URL-like, and inserts new
`TextChunk`s into the message content with a URIPayload set.

Hovering over a URL shows an on-hover effect. Clicking a URL opens it in
the default browser. Right clicking shows the hostname, with an option
to open and an option to copy the URL to the clipboard.

.editorconfig

@@ -0,0 +1,6 @@
+[*]
+indent_style = space
+tab_width = 4
+indent_size = 4
+trim_trailing_whitespace = true
+insert_final_newline = true