docs(readme): launch refresh — new screenshots + copy aligned with the blog post

Replace the README screenshot set with the staged Honeycomb Studios
assets from the launch blog post. The previous hero showed a real
internal community (internal channel names, employee avatars, and an
in-flight auth-boundary discussion) and predated the forge UI.

- Hero: engineering channel — humans and agents sharing code, test
  results, and a release decision
- Gallery: agent swarm coordination + Git forge PR view (new),
  media comments retained; agent-member and create-channel shots removed
- Copy: lead with the coordination thesis; 'authorization does not
  erase authorship' in the agent bullet; Git bullet now separates what
  ships today (hosting + early forge UI) from branches-as-rooms
- Status table: forge UI, huddles, and Buzz Mesh added to works-today;
  push notifications moved to being-wired-up (gateway shipped in #1770)
- Fix stale 'four vision docs' (there are seven); link buzz.xyz;
  one architecture sentence on CAS packfiles + TLA+-checked pointer swap
- seed-admin-dashboard.sh: repoint fixtures at the new image files

Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>

scripts/seed-admin-dashboard.sh

@@ -78,8 +78,8 @@ upload_fixture() {
 
 fixture_dir="$(mktemp -d "${TMPDIR:-/tmp}/buzz-admin-feedback.XXXXXX")"
 search_image="${REPO_ROOT}/docs/assets/screenshots/media-comments.png"
-workspace_image="${REPO_ROOT}/docs/assets/screenshots/channel-thread.png"
-quality_image="${REPO_ROOT}/docs/assets/screenshots/channel-agents.png"
+workspace_image="${REPO_ROOT}/docs/assets/screenshots/engineering-channel.png"
+quality_image="${REPO_ROOT}/docs/assets/screenshots/agent-swarm.png"
 composer_diagnostics="${fixture_dir}/composer-diagnostics.txt"
 workspace_diagnostics="${fixture_dir}/workspace-diagnostics.txt"
 trap 'rm -f "${composer_diagnostics}" "${workspace_diagnostics}"; rmdir "${fixture_dir}"' EXIT