- Remove tool_choice from AgentEndpoint (create, update, list responses)
- ChatService: automatically set tool_choice='any' when workspace, memory
or skills present, null otherwise. Same for preparer/review/finalizer
- SystemPromptBuilder: remove 3 toolAny-conditional prompt blocks
(KRITISCH, Verhalten, ERINNERUNG)
- Frontend: remove checkbox, badge and JS references
- Agent.ToolChoice DB field preserved for backward compat, no longer read