Groups: make, join, run and leave communities and circles

The Groups page (/groups, in the menu) is where a persona makes a community
or a circle (with its invitation code and an optional password), joins one
by invitation and leaves one. For the groups it runs it edits them, shows
the invitation, lets in or declines the requests to join, and takes members
out, through PrivaPub's new /clientapi/group/members, reject and remove.
The e2e makes a circle, joins it as another persona with the code, and has
the owner take that member out.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

CLAUDE.md

@@ -232,6 +232,10 @@ supplies:
 - **Profiles and search** (`Pages/Profile.razor` at `/account/{id}`, `Pages/Search.razor` at `/search?q=`): a card's
   author and a notification's account open the profile in the app; "Open original" is the only way to the remote site.
   A card in a fixed-height flex column with `overflow-hidden` needs `flex-none`, or it collapses to nothing.
+- **Groups** (`Pages/Groups.razor` at `/groups`): the persona's communities and circles (`GroupService`, `/clientapi/group`):
+  made (a circle unless it is a community, with an invitation code and an optional password), joined by invitation and
+  left; the ones it runs edited, their invitation shown, the requests to join let in or declined, members taken out.
+  Only a group's owner and moderators see who is in it.
 - **Lists** (`Pages/Lists.razor` at `/lists`): made, renamed, given a replies policy and made exclusive (their members
   leave the home feed) there, filled from the accounts the persona follows; a followed account's profile has a Lists
   menu too. A list is read as the feed's Lists tab (`FeedFilter.ListId`). Lists never leave PrivaPub.