fix(tmux): merge-time fixes for the exited-agent report (#466)

- docs/wiki/The-Dashboard.md: the tab-appearance table gains the exited
  state (muted dot plus an `exited (137)` badge) and explains the bare
  `exited` variant.
- The detailed sidebar and rail no longer pair the muted dot with an "idle"
  pill: an exited session's pill reads "exited" (neutral styling) and its
  since stamp measures from the observed exit. This is a label override on
  the row model, not a new state, so SESSION_ACTIVITY_RANK and the home
  screen order are untouched, and a pending alert still keeps its own pill.
  The row signature includes the flag so the incremental path repaints it.
- The exited badge is aria-hidden like its sibling badges, and the exit is
  appended to the tab's aria-label in both render paths through one helper.
- test/tmux-manager.test.ts re-adds the junk-trailing-field parser case
  against parsePaneRows.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/wiki/The-Dashboard.md

@@ -48,6 +48,7 @@ One tab per session, in your order, and that order syncs across your devices.
 | Yellow tab, blinking          | The agent is waiting for input from you.                                 |
 | Red tab, blinking             | A question or permission prompt is blocking the session.                 |
 | No dot                        | The session is not running.                                              |
+| Muted grey dot plus an `exited (137)` badge | The agent inside the pane has exited, with that exit code (or `exited (signal 9)`). A bare `exited` means tmux saw the pane die but did not report how, which is not the same as a clean `exited (0)`. Detailed sidebar and rail rows read `exited` in their pill. |
 
 ![Tab alerts](https://raw.githubusercontent.com/Ark0N/Codeman/master/docs/images/tab-alerts-20260815.png)