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>

src/web/public/styles.css

@@ -18429,6 +18429,15 @@ html[data-tab-orientation='vertical'][data-tab-rail-detail='rich']:not(.tab-rail
   color: color-mix(in srgb, var(--green) 45%, var(--text-muted));
 }
 
+/* An exited agent (Ark0N/Codeman#446): neutral, like the muted dot beside it.
+   No green at all, since nothing is running behind this row. */
+html[data-sidebar-detail="rich"] .session-sidebar .tab-pill--exited,
+html[data-tab-orientation='vertical'][data-tab-rail-detail='rich']:not(.tab-rail-compact) .tab-rail .tab-pill--exited {
+  background: color-mix(in srgb, var(--text-muted) 10%, transparent);
+  border-color: color-mix(in srgb, var(--text-muted) 30%, var(--border));
+  color: var(--text-muted);
+}
+
 /* Accent, deliberately none of the three above: a watching session is waiting for
    work it started itself, not for the user, and the red and yellow here are spoken
    for by sessions that ARE waiting for the user. */