Fixed: "Focus on one project" showed nothing. Claude's sidebar renders
only a few recent chats, so hiding alone left it empty. Focus mode now
adds the selected project's chats to the sidebar.

Fixed: Cowork sessions were never filtered in any mode. They are not
part of a project, so focus mode now hides them in the sidebar and on
the Chats and tasks page.

Fixed: focus mode with no project selected silently did nothing. The
popup now says a project needs picking.

Fixed: "Focus on one project" silently did nothing until a project was
actually picked in the dropdown, with no indication that a selection was
needed. The popup now shows "Pick a project - nothing is hidden until you
do." while no project is selected.

Also documented Chrome/Chromium installation in the README. No extension
behaviour changes for Firefox users beyond the fix above.

Fixed for Claude.ai's redesigned sidebar. The extension now:
- Works with the new sidebar (chats are matched by their new markup instead of the old link format)
- Also filters the "Chats and tasks" page, which switched to a table layout
- Now includes starred chats when hiding project conversations
- Covers your full chat history instead of only the 100 most recent chats
- Keeps a Project's own chat list fully visible on its page (including the new /cowork project pages)

Adds "Focus on one project" mode: show only chats from a selected project
and hide everything else. Existing behavior is preserved as the default
"Hide project chats" mode. New "Off" option pauses hiding without removing
the extension.