/flow redirects to /boards and the top bar drops its Flow button #2767

Rest of the former #2693.

Done:

• [ ] GET /flow answers 301 to /boards (the held panel)
• [ ] the top bar keeps search, New and the user menu, and no Flow button
• [ ] test/crew-held.test.ts's "both doors" reads the web door from /boards and keeps the terminal's Flow dialog. Say in the pull that the test moved with the page
• [ ] remove /flow from forge.json app.looks if it is listed

Run test/crew-held.test.ts before pushing.

Parked by the crew: the check failed ("the merge queue > the queue shows through every door: /flow, the terminal and MCP, while gating and after") and the decider saw no point in another try (pull #2788 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: the check failed ("design check: nothing added outside the system (#2678) > the tree is no worse than its baseline") and the decider saw no point in another try (pull #2791 closed).

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the check failed ("the merge queue > the queue shows through every door: /flow, the terminal and MCP, while gating and after") and the decider saw no point in another try (pull #2788 closed)
2. the check failed ("design check: nothing added outside the system (#2678) > the tree is no worse than its baseline") and the decider saw no point in another try (pull #2791 closed)

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Split. Both pulls broke tests that fetch /flow (test/merge-queue.test.ts and about nine others), and the second also added styling outside DESIGN.md. #2807 moves those tests to /boards first and leaves /flow serving its page. #2808 then redirects /flow and removes the button, adding no styling, and waits for #2807.