First-run onboarding: guide a fresh account to the workbench picker, not an auto-minted empty one

[TheGreatAxios]

Summary

• Fixes CL-6555. Logging into a brand-new account used to auto-mint a blank, unlabeled "New Workbench" (CL-6138) and land straight in it — no explanation of what the room is for, and no guided path. HomeRoute's zero-workbench branch now waits for Myra's readiness (same wait/slow/retry UX from CL-6457/CL-6462, unchanged) and then navigates to the existing NewWorkbenchPickerRoute (/new) so a fresh account creates its first real workbench there — template or "Just start talking" — the same picker every other "+ New workbench" control already uses.
• Removes the now-dead createAgentAndLaunch (the one-off auto-mint verb this replaces) and its tests.
• Accounts that already have one or more workbenches are unaffected — unchanged ensureMyraWorkbench path.

Root cause investigated

The reachable creation paths (POST /workbenches with a definitionId) are atomic server-side — the route compensates (deletes the workbench) if the agent join fails, so a workbench minted that way always has an agent participant. So the literal "type and nothing answers" state isn't reachable through today's standard fresh-account flow. It is architecturally real but latent elsewhere: sendWorkbenchMessage never rejects a send, default-routing falls back to a workbench's "host" (first agent participant), and if there is none the message is durably posted but never routed — silently. provisionSpaceWorkbench already creates intentionally participant-less kind: "workbench" rows (routine spaces), proving the codebase tolerates this shape elsewhere. Filed as a scoped follow-up in CL-6555 rather than bundled into this change, since it touches the backend fan-out/notice path and the standard creation path already guards against it.

Test plan

• bun test test/home-page.test.tsx src/instant-agent-create.test.ts (apps/web) — all pass
• bun test ./src ./test (apps/web, full suite) — 833 pass, 0 fail
• bun run typecheck (apps/web) — clean
• bunx eslint on changed files — clean
• bun run check:structural — all checks pass
• New test: a brand-new account with zero workbenches lands on /new, not an auto-minted room
• Regression test: an account with an existing workbench is unaffected (still lands via ensureMyraWorkbench)
• Existing wait/slow/retry-after-connecting-a-provider tests updated and passing against the new redirect target

https://linear.app/abklabs/issue/CL-6555