feat(web): write descriptions and comments with a visual editor

ts-rich-editor (TipTap) shows the formatting while writing: bold,
italic, strike, code, headings, lists, task lists, quotes, code blocks
and links, with @ suggesting the project's members and pasted
screenshots uploaded as attachments. It reads and writes the same
Markdown the API keeps (mentions as @[Name](id), images as
attachment:<id>, tables too), so nothing already written changes.

Used for comments, replies, editing a comment or a description, a new
ticket from the board and the public proposal form; the Markdown hint
and the paste directive are gone. List markers sat on a line of their
own, and task lists showed a stray bullet, in the editor and when read.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/presenters/src/lib/pages/issue.page.scss

@@ -445,30 +445,6 @@ a.ts-key {
   margin: 0.5rem 0;
 }
 
-.ts-mentions {
-  display: flex;
-  flex-wrap: wrap;
-  gap: 0.375rem;
-}
-
-.ts-mentions__option {
-  display: inline-flex;
-  align-items: center;
-  gap: 0.5rem;
-  padding: 0.25rem 0.625rem 0.25rem 0.25rem;
-  border: 1px solid rgba(127, 127, 127, 0.3);
-  border-radius: 999px;
-  background: transparent;
-  color: inherit;
-  font: inherit;
-  cursor: pointer;
-}
-
-.ts-mentions__option:hover,
-.ts-mentions__option:focus-visible {
-  border-color: currentColor;
-}
-
 // Code that mentions the ticket (from the Git integration).
 .ts-dev {
   display: grid;