feat: extend herdr dispatch to pi/codex/copilot and reuse the running workspace

Added

• CREW_HERDR_ENABLED=1 now works for pi/codex/copilot, not just claude.
  dispatchViaHerdr's gate on platform === "claude" is gone — herdr's own --kind already
  supports all four (herdr agent start --help), and its idle/working/blocked/done detection
  is generic per kind, so only the per-platform interactive argv, trust-dialog text, and
  reply-extraction markers were claude-specific. pi and copilot were verified live against
  herdr 0.8.2 (pi launches with --approve, which skips its trust prompt outright rather
  than needing one answered; copilot's own "Confirm folder trust" dialog is a new
  HERDR_DIALOGS entry). codex could not be verified live (no credentials in the environment
  this was built in to get past its sign-in screen) — its argv is built from documented flags
  only, and its reply-extraction falls back to pi's glyph-less heuristic; an unrecognised
  first-run dialog still fails loud rather than guessing a keystroke, same as an unmatched
  dialog on any other platform.

• CREW_HERDR_ENABLED=1 reuses the workspace crew-afk itself is running in, if there is
  one, instead of always opening a new one. herdr injects HERDR_WORKSPACE_ID into any
  pane it manages — so when a human starts crew-afk from inside a herdr-managed session,
  ensureHerdrWorkspace now adds the sprint's dispatch tabs straight into that same
  workspace rather than popping open a second, unrelated one. A workspace crew-afk didn't
  create is never closed at the end of the run either — only one this run created itself is.