2ba84c5ba0
PRD 0021 chunk 4 (final). Two adjustments to close the
split-pane loop:
1. `_stop_bottle_flow` clears `tmux_state['slug']` when the
stopped bottle was the right-pane occupant. The pane itself
stays in place (claude exits with "container not found");
the operator presses Enter on a different agent to
repurpose it via respawn-pane.
2. `_render` accepts `right_pane_slug` and marks the matching
agents-pane row with a `*` prefix + A_BOLD (when it's not
also the focused row — focused selection still wins for
visibility). Gives the operator a clear visual link
between which agent the dashboard says is "active right
now" and which one is visible to their right.
Wired through `_main_loop`: passes `tmux_state` to
`_stop_bottle_flow` on `x`, and `tmux_state.get('slug')` to
`_render` on every tick.
479 unit tests pass (1 new for the tmux_state-preservation
on non-owned stop). PRD 0021 implementation complete pending
merge.