Workflow: group-like chat with Bot flowchart + assign tasks to a pipeline #1318

Summary

Add Workflows that look like FlyBot group chats, with a flowchart of Bots (sequence + fork/join) editable by visual drag-drop. Tasks on the board can run on a Workflow; Bots can invoke Workflows; board tasks auto-assign to a matching Bot or Workflow when a match exists.

Owner HTML demo remains visual reference for the chat/flowchart shell (/workspace/flybot-workflow-demo/).

Product (owner 2026-10-27)

1. Predefined Workflows — ship/fixture a few named templates (e.g. 发布交付流水线: Planner → Writer → Coder → (Reviewer ‖ Tester) → Deployer).
2. Bot-defined Workflows — a Bot (or owner via UI) can create/edit a Workflow graph (drag-drop editor; persist). Not JSON-only as the primary path.
3. Bot can call a Workflow — tools / board actions so a Bot starts a named Workflow run (with task / brief), not only human UI.
4. Kanban auto-assign — when a board task is created/updated, if it matches a Bot or a Workflow (rules: tags, title/keywords, assignee hint, workflow trigger filters — implement a clear v1 matcher + tests), assign automatically and start execution; unmatched stays for manual assign. Manual "assign to Bot / Workflow" remains.
5. Shell: Workflow session ≈ group chat; Details/流程图 shows run status + edit mode; DeepSeek --bt-*; Chinese primary labels.

Done when

• Templates exist; owner/Bot can create/edit graph via drag-drop and persist.
• Bot tool (or equivalent) can start a Workflow run.
• Board matcher auto-assigns matching tasks to Bot or Workflow and kicks off work; non-match does not force-assign.
• Run progress appears in Workflow chat + flowchart status.
• Tests: graph edit/persist, sequential+parallel advance, bot invoke, auto-assign match/miss.
• Docs + CHANGELOG fragment.

Out of scope (v1)

• Cross-home / friends' Bots as Workflow nodes.
• Prod deploy (owner yes separately).

Notes

• PR: Fixes #1318. Claim: Birfy.
• Expand from earlier demo scope; prefer solid v1 matcher (document rules) over opaque ML.