feat(groups): editable description, and one source of operator authority

A description could only be set the moment a group was created, so every
group made before anyone thought of one stayed blank for good. The owner
can now edit it from the group's page, and PATCH /v1/groups/{id} takes it.

That endpoint takes the description and nothing else, deliberately. The
name, the visibility and the join policy are the terms members joined on;
a private group that can quietly become public is not the group they
agreed to be in. Changing those needs a decision about who gets told, not
a field on a form — there is a test saying so.

Separately, the legacy operator key is gone. `admin_pk_ed25519` in
node.toml named the operator before the roster existed and was kept so
that an existing deployment would keep working; nothing uses it, and a
second source of node authority is not something to carry around out of
politeness. Authority is the roster, read fresh on every check.

It is removed rather than ignored: a config that still names the key gets
a warning at startup pointing at the file. Dropping it in silence would
refuse invites and file deletion with a signature error that looks like a
bug somewhere else — which is exactly how finding M3 presented.

Two tests were verifying admin operations by naming a key in the context,
which was the legacy path. They now pair an operator into a roster, the
way an operator does. The authority test anchored on the deleted function
and passed vacuously once it disappeared; it states the invariant against
the verifier and the daemon instead.

Also defined .btn-secondary, used in four places and styled in none.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/groups.py b/packages/meshbay-hub/src/meshbay_hub/api/groups.py
index 43d72c3..83feeb4 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/groups.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/groups.py
@@ -276,6 +276,38 @@ async def create_group(
     return {"group_id": group.id, "name": group.name}
 
 
+class GroupUpdateRequest(BaseModel):
+    description: str | None = None
+
+
+@router.patch("/{group_id}")
+async def update_group(
+    group_id: str,
+    body: GroupUpdateRequest,
+    current_user: User = Depends(require_user_scope),
+    db: AsyncSession = Depends(get_db),
+):
+    """
+    Change the group's description. Owner only.
+
+    Only the description: name, visibility and join policy are what members
+    joined on the strength of, and a group that can quietly become public is a
+    different thing from the one they agreed to. Those need a decision about who
+    is told, not a PATCH.
+    """
+    group = await db.get(Group, group_id)
+    if not group:
+        raise HTTPException(status_code=404, detail="Group not found")
+    if group.admin_id != current_user.id:
+        raise HTTPException(status_code=403, detail="Only the group owner can edit it")
+
+    if body.description is not None:
+        desc = body.description.strip()[:512]
+        group.description = desc or None
+    await db.commit()
+    return {"group_id": group.id, "description": group.description or ""}
+
+
 @router.post("/{group_id}/members/{username}", status_code=201)
 async def add_group_member(
     group_id: str,