Remove the Flow only toggle: the `flow` label alone says what goes first #7636

Owner, 2026-11-01: "that flow setting is trash... i like the idea of controlling flow with labels a lot however a toggle for that is bad and doesnt make sense." The owner read the switch as "work the open roadmap and make nothing new". It did the opposite: it stopped builders starting unlabelled issues and left the planner running. On 2026-11-01 it held 80 ready issues with no flow issue open, and looked like the forge had gone to sleep.

New shape, no switch, no state: ready issues labelled flow go first. When none is ready, builders take other ready work as usual. Nothing is ever held by a mode, so idling with ready work becomes impossible by construction.

Done when:

• [ ] The dispatcher orders ready issues with flow first, in one place, and a test shows labelled work starts before older unlabelled work, and that with no labelled issues unlabelled work still starts.
• [ ] The toggle is gone from every surface: src/web/studio/crew.ts, the home clog button (#6395), flow_only_line, the flowOnly field in the API and MCP, the auto let-go in src/flow/flow_only_auto.ts, and the flow_only_watch table. Delete the code rather than hide it. A repository with the switch on today simply stops holding.
• [ ] Issues already held show no "queued: flow only" line, and held assignments run.
• [ ] Applying the label is one click from an issue and a list, and the MCP labels tool does the same. The ready list shows labelled work on top, so a person sees what goes next.
• [ ] A planner that keeps adding issues is a separate question and is not part of this.

Supersedes #7629.

Parked by the crew: the check failed ("migrations are additive across a roll > every migration not in both releases still in play is additive") and the decider saw no point in another try try 1: README.md, docs/MCP.md, docs/STATUS.md, docs/design/areas/flow-first.md (+53 more) (pull #7674 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.

Owner's conductor: reopened pull #7771, please finish it. One red left: "an agent pull that waits for a person's review says so > the board and the autonomy settings say so". The toggle moved around that text in src/web/studio/crew.ts, so it looks like this pull's own: restore what the test wants, or update it if the wording moved on purpose. The owner asked for this toggle to go.

Owner's conductor: reopened pull #7771 once more. The last push fails to boot: "start: exited with code 1 before answering — error: Unexpected <<". That looks like a conflict marker committed by the merge. Search the branch for <<<<<<< and fix it, then merge main once more. Please land this one small: it is only the toggle's removal.