feat(teams): add multi-agent team support with TL, bidding arena, and blackboard

[moyunqinghe]

Summary

Adds multi-agent team support: teams of digital employees with a Team Lead (TL), task assignment/claiming, a 3-round HP-based bidding arena, a per-team blackboard, and full HITL (human-in-the-loop) controls. Design decisions are documented in design-multi-agent-team-decisions.md.

Backend

• New app/teams/ module: teams/members CRUD, task lifecycle (pending → bidding → in_progress → review/rework → done/cancelled/escalated), bidding with per-round TL scoring and HP elimination, blackboard ingest pipeline (parse → normalize → structured write → citations), wake events, and audit trail (team_task_events)
• 7 new tables (SQLite ALTER/CREATE migrations in db/database.py), optimistic locking on task claim/award
• Team TL chat integrated into the workspace chat: ChatSession.team_id, team-context injection (roster / open tasks / blackboard top-K) and task-dispatch post-processing in /api/chat/turn and /api/chat/stream
• Channel bindings can target a team; inbound messages to a team-bound channel get TL semantics via service_intake.py (merged with the new inbound attachment support)
• New blackboard query tool available inside member execution sessions

Frontend

• New pages: TeamsPage, TeamDetailPage (task board, bidding records, reports, award override), TeamChatPage; BiddingArena and TeamCard components; sidebar navigation entry
• Agent-scope storage extended with team scope (isTeamScope / readEmployeeScope); chat header/empty-state updated for team sessions
• Knowledge detail dialog gains a graph view (KnowledgeGraphCanvas) with a graph/cards toggle — this intentionally coexists with the new overview-panel KnowledgeGraphVisualization
• i18n entries for all new UI text (zh source + en translations)

Explicitly out of scope (v1): pure-agent resident TL loop, unbounded debate, automatic cross-team information flow.

Risk

• Large surface area (~15.6k insertions), but nearly all additive; existing single-agent paths are untouched. Shared-file changes are limited to scope-storage handling and additive fields (ChatSession.team_id, ChatTurnRequest.interaction_mode)
• DB migration is SQLite-only, matching the supported production migration path
• Rebased onto latest main; conflicts resolved in service_intake.py (attachments + team context both preserved), KnowledgePage.tsx (both graph views kept), and en.json (both translation sets kept)

Tests

• pytest backend/tests: 1478 passed (incl. 7 new team test modules)
• npm --prefix frontend-enterprise test: 145 passed
• npm --prefix frontend-enterprise run build: passes
• ruff check: no new violations beyond patterns already present in the codebase (e.g. FastAPI Depends B008); i18n:check failure count is lower than on main (pre-existing failures unrelated to this PR)

UI validation

Routes verified locally with an admin user: /teams, /teams/:id (board, bidding arena, award override), team TL chat via /workspace/chat/:sessionId, and the knowledge detail graph view.