Add a persisted "Link preview" toggle (default on) to the memo
display-settings popover, mirroring the compact-mode setting. When turned
off, link-preview cards are hidden across all memo views and the metadata
request is skipped (the gate sits at the paragraph renderer and reads the
preference from ViewContext). Resolves the request in #6045.
Memo list views hard-coded compact rendering, truncating long memos by
default. Make full content the default and add a persisted 'Compact mode'
toggle (default off) in the display-settings popover, backed by the
localStorage ViewContext. Wire Home/Explore/Archived/UserProfile to read
it; add the compact-mode label across all locales.
Add a rich-text formatting toolbar as the focus-mode header when the
WYSIWYG editor is active: heading dropdown, bold/italic/code, lists, and
link, with a priority+overflow responsive layout and live active-state
highlighting. The toolbar is a self-contained component driven through a
new FormattingController surface routed via EditorContent.
Remove the now-redundant slash-command feature (/todo, /code, /link,
/table) and its "Type / for commands" hint, since the toolbar covers
those actions; the shared suggestion renderer stays for #tag.
