refactor(web): rename room identifiers to workbench (CL-8586)

[TheGreatAxios]

Summary

• "Room" is not product vocabulary; the child tenant is a workbench. Mechanically renames every identifier, file, route, CSS class, and comment that used "room" to its workbench equivalent.
• Genericizes the vendoring ledger's owner column and a stray fixture domain.

Changes

• Renamed files: room-roster.ts/.test.ts → workbench-roster.ts/.test.ts, workbench-room-page.tsx → workbench-page.tsx.
• Renamed types/functions across apps/web/src (chat, pages, shell) and packages/error-sink: e.g. RoomParticipant → WorkbenchParticipant, RoomMessage → WorkbenchMessage, sendToRoom → sendToWorkbench, listRoomParticipants → listWorkbenchParticipants, readRoom/readRoomFolder → readWorkbench/readWorkbenchFolder, roomKeys → workbenchKeys, redeployRoomAgent → redeployWorkbenchAgent, WorkbenchRoomRoute → WorkbenchRoute, roomId → workbenchId.
• Renamed CSS classes (room-info-*, room-main*, room-layout, room-subthread*, room-participants, room-replies-link) to workbench-* equivalents.
• Updated test fixtures (tnt_room → tnt_workbench, room.example → example.com).
• Left literal English uses of "room" (breathing room, room for a fourth column, etc.) as prose, rewording a few to avoid the bare word for a clean grep.
• VENDORED.md: owner column sawyer → maintainers.

Testing

• bun run check (typecheck, lint, fmt, test) passes.
• grep -rniI room over apps/web/src, packages, agents, workflows, docs, and root *.md (excluding vendor/node_modules/dist) returns zero hits.

[linear-code]

CL-8586