docs: consolidate Bruno collections into top-level bruno/
apps/appview/bruno/ was a leftover from when the admin role endpoints
were first written. The top-level bruno/ collection was created later
but never picked up the three files that already existed:
- Admin/Assign Role.bru
- Admin/List Members.bru
- Admin/List Roles.bru
Move all three into bruno/AppView API/Admin/ alongside the backfill
endpoints. Remove the now-redundant apps/appview/bruno/bruno.json and
environments/local.bru.
Add missing environment variables (target_user_did, role_rkey) to both
local.bru and dev.bru so Assign Role.bru resolves correctly.