v0.20.0 — Enter opens an agent's real CLI, interactively

og agents listed your agents but could not get you to them. Every row is now
selectable — the orchestrator included — and Enter focuses a tab holding that
agent's real CLI, interactively: a vendor CLI's blocking permission prompt
can be answered in the terminal instead of opening the web UI to do it.

Added

• Enter opens an agent's real CLI in its own tab. Native agents (Claude
  Code, Codex) get the vendor TUI; ACP agents get their own
  omnigent attach view — the same one og chat's down-arrow menu shows. The
  tab is created on demand the first time you ask for it, and pressing Enter
  again returns to the same tab rather than opening another.
• The orchestrator row is selectable. Root rows could not be reached at all
  before, so selecting claude and landing in Claude Code was impossible.
• Terminal discovery asks the runner. og scanned $TMPDIR for a
  bridge.json/tmux.json pair, which only ever worked for claude-native —
  a codex sub-agent writes no tmux.json and was unreachable. Discovery now
  asks the runner for the session's terminal resources, keeping the scan as a
  fallback so nothing regresses when the runner is unreachable.
• The agents pane is themed by role — footer keys and labels, the access
  panel, and a · separator drawn from the active theme.

Changed

• Enter focuses the selected agent's own tab, not its root. Selecting a
  worker used to focus the conversation it belonged to.
• Esc clears the selection; q is the only quit. Esc used to quit.
• space expand is gone — Enter supersedes it.
• r refresh is gone — the pane already polls on its own timer, so r
  only skipped the wait.
• The footer is now ↑/↓ move ∙ ⏎ focus ∙ t theme ∙ a access ∙ q quit,
  measuring 50 / 30 / 20 columns against the 80-column ceiling. Esc is bound
  but deliberately unlisted.
• The tmux attach is interactive. It kept tmux's read-only,ignore-size
  pair where only ignore-size was load-bearing — that is what stops a narrow
  client resizing and corrupting the live agent's TUI, and it still does.

Fixed

• Selection dimming was a one-way door. Pressing an arrow key dimmed every
  unselected agent, and nothing brought the list back — it stayed dimmed for
  the rest of the session.
• herdr started its server after the case-(B) attach rather than before it.
• The access panel no longer draws dimmed, and fills its pane.
• The footer strip no longer paints over the selection's cell, and uses a
  Narrow separator (none in the compact form) so the measured widths hold.

Docs

• docs/HERDR.md documents how a tab's pane is routed by harness kind.
• The tab.create timeout case is recorded where it happens: a create that
  times out may still have landed, leaving a rare orphan tab. It is not
  specific to this path — every create in og has it, because the herdr protocol
  has no idempotency key — and reconciling by tab label is deliberately not
  done, since the label is the harness product name and is not unique per
  session, so it could close another agent's tab.

---

All of #37, #38, #39 and #40. Gate on the release commit: pytest tests/
1486 passed, 0 failed, bash -n and shellcheck -S error clean.