Workflow orchestration follow-ons: group workflows, SimpleChat action parity and plan replay #1550

Summary

Part of #1543 (Phase 8). Follow-on work after the personal-workflow phases ship. Each item is scoped separately when it starts and may become its own issue.

User Value

v1 covers personal workflows only, and workflow tasks can't use every orchestration capability. These follow-ons bring the same experience to group workspaces and to the SimpleChat action, and let scheduled work use web search, deep research, file rendering and images.

Proposed Behavior

• Group workflows: group roles, eligible Run-as members, allow_group_workflows and group assignment. This also turns on Ask AI for group workflows, which Phase 3 hides.
• Update the SimpleChat action for task-based workflows and reorganize its capability list #1347: the SimpleChat action creates task-based workflows through the Phase 2 draft service.
• Plan-replay workflow task (M5C O2): a task that replays a frozen, approved orchestration plan. It closes the vocabulary gap (web search, deep research, render_file, images) but needs a delegated-identity design for scheduled orchestration.
• Design generic monitor trigger model for workflows #949 generic monitor triggers stay a separate design.

Acceptance Criteria

• Each follow-on is scoped, and either shipped or split into its own issue linked here.
• Group workflows created from chat honor group roles and Run-as eligibility.
• Docs, tests, release notes and a config.py version bump for each shipped item.

Notes

• Roadmap: §6, Phase 8. Related gotchas in §8: 3 (vocabulary mismatch), 29 (group workflows in the shared editor).
• M5C handover: docs/explanation/features/WORKFLOW_M5C_COMPLETION_AND_NEXT_STEPS.md.
• Depends on: Phase 4 (Let chat orchestration propose workflows with an Approve, Deny and Edit card #1547) and later phases.
• Related: Update the SimpleChat action for task-based workflows and reorganize its capability list #1347, Design generic monitor trigger model for workflows #949, Generalize workflows into repeatable AI automations without required documents #1082, Split Microsoft 365 actions with sharing approvals, live file RAG, and delegated workflow execution #1493.