Delete dead Multi-Agent GAgents and demote Studio Empty-state generators

[eanzhao]

Goal

Reduce the number of GAgent types in the repo by removing actors that are either dead code or stateless-shaped (AIGAgentBase<Empty>), per CLAUDE.md "Actor 即业务实体；删除优先".

Inventory (verified 2026-05-14 on feature/lark-bot)

A. Dead code — zero callers

GAgent	File	Verification
TaskBoardGAgent	src/Aevatar.Foundation.Core/MultiAgent/TaskBoardGAgent.cs	grep matches only own file + docs/adr/0006-multi-agent-evolution.md + audit doc + own test
TeamManagerGAgent	src/Aevatar.Foundation.Core/MultiAgent/TeamManagerGAgent.cs	same — zero production callers

Both are residue from the Multi-Agent experiment (ADR-0006). Cross-references loning's framing in discussion #568 ("ChatRuntime/Memory/Governance/TaskBoard 都不该存在").

B. Stateless伪 actors — AIGAgentBase<Empty>

GAgent	File	Why suspect
ScriptGenerateGAgent	src/Aevatar.Studio.Hosting/Endpoints/ScriptGenerateGAgent.cs	AIGAgentBase<Empty> — no persistent state
WorkflowGenerateGAgent	src/Aevatar.Studio.Hosting/Endpoints/WorkflowGenerateGAgent.cs	same

These wrap one-shot Studio AI generation. Empty state means no event-sourced fact is owned — they're stateless services in an actor shell.

Proposed actions

Phase 1 — delete dead code

• Delete TaskBoardGAgent, TeamManagerGAgent, their .protos (multi_agent_state.proto), ports, projectors, tests
• Mark ADR-0006 superseded with rationale (kept for history)
• CI guard: add Aevatar.Foundation.Core.MultiAgent.* to banned-namespace check so nobody re-adds it

Phase 2 — demote stateless generators

• Convert ScriptGenerateGAgent + WorkflowGenerateGAgent into stateless application services (e.g. IScriptGenerateService / IWorkflowGenerateService)
• Move LLM call to the service; keep the existing *ActorService HTTP wrapper or fold it in
• Tests: golden-path generation still works

Out of scope

• Run/Session base class refactor (LlmSessionGAgent/ResponseSessionGAgent + ServiceRunGAgent + WorkflowRunGAgent + ScriptEvolutionSessionGAgent sharing a generic base) — separate proposal; that reduces code duplication but does not reduce GAgent type count
• Merging Service* (7 types) or Script* (5 types) — each is a distinct aggregate root; CLAUDE.md "Actor 即业务实体" forbids collapsing

Expected outcome

• GAgent type count: 25 → 21
• Cross-references issue for /v1/messages (Path B) which intentionally adds zero new types

Risk

• Audit any external aevatarAI/aevatar consumers for TaskBoardGAgent / TeamManagerGAgent references before deleting
• Studio integration tests against the demoted services must cover the same surface