feat(hub): group names unique per owner, shown as name@owner

A group's identity stays its UUID. What changes is that "the name is
unique" — until now an unenforced expectation — becomes real, scoped to the
owner account, and the owner's username is surfaced so two groups called
"photos" on different nodes can be told apart.

Hub:
- `groups` gains a functional unique index `uq_groups_owner_name` on
  `(admin_id, lower(name))` (model + migration c3d4e5f6a7b8). The migration
  pre-flights: if the data already clashes it aborts and lists the
  offending (admin_id, name) pairs rather than renaming anyone's group.
  meshbay.org checked clean.
- `create_group` trims the name, rejects blank (422) and an owner-scoped
  case-insensitive clash (409), with an IntegrityError backstop for the
  race, and returns `owner_username`.
- `owner_username` added to `/v1/groups/mine`, `GET /v1/groups` (local
  rows), `POST /v1/groups/{id}/join`, `GET /v1/admin/groups`.

SPA:
- new `static/group-name.js` — `<GroupName name owner [inline]>` renders the
  name with the `@owner` handle on a smaller grey line under it.
- used in the sidebar, the group-page header, Explore cards, the Admin
  groups table, and cross-group Search (via a widened `cacheGroupIndex`
  carrying the owner). Delete/leave confirmations show `name@owner` inline.
- federated Explore rows show `@<source_hub>` instead of an account.

Design record and the locked decisions: ~/next/groupnames.md (out of repo).
MNP unchanged. Tests: test_group_name_unique.py, test_group_name_migration.py.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018gKJ85aZyvEwarXMFzFEwi

1 files changed, 22 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/group-name.js b/packages/meshbay-hub/src/meshbay_hub/static/group-name.js
new file mode 100644
index 0000000..af8879c
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/static/group-name.js
@@ -0,0 +1,22 @@
+import { html } from './vendor/htm-preact.js';
+
+/**
+ * A group's name with the `@owner` handle under it.
+ *
+ * Group names are unique only per owner account (the hub enforces that), so the
+ * `@handle` is what tells two groups called "photos" apart. `owner` is the
+ * owner's username for a local group, or the source hub for a federated one
+ * (decision 5 in ~/next/groupnames.md); the caller decides which.
+ *
+ * `inline` renders "name@owner" on one line, for places that cannot take a
+ * block — a badge, a `confirm()` string built elsewhere.
+ */
+export function GroupName({ name, owner, inline = false }) {
+  if (inline) return owner ? `${name}@${owner}` : name;
+  return html`
+    <span class="gn">
+      <span class="gn-name">${name}</span>
+      ${owner && html`<span class="gn-owner">@${owner}</span>`}
+    </span>
+  `;
+}