Fix panic and stale mission view on detail dismiss

Two bugs:
1. DismissByID panicked with 'makeslice: cap out of range' when the
   session wasn't in the tasklist (empty list → cap of -1). Fixed by
   using len(m.sessions) as capacity instead of len-1.

2. Mission view wasn't updated after dismiss because viewMode was set
   to ViewModeMission *after* recomputeAndDisplay ran. Since recompute
   only pushes data to the active view, mission never got the updated
   session list. Fixed by setting viewMode before recompute.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: maxbeizer

internal/tui/components/tasklist/tasklist.go

@@ -400,7 +400,7 @@ func (m *Model) DismissByID(id string) {
 		m.dismissedStore.Add(id)
 	}
 	// Remove from current sessions
-	newSessions := make([]data.Session, 0, len(m.sessions)-1)
+	newSessions := make([]data.Session, 0, len(m.sessions))
 	for _, s := range m.sessions {
 		if s.ID != id {
 			newSessions = append(newSessions, s)

internal/tui/keyhandlers.go

@@ -332,8 +332,8 @@ func (m Model) handleDetailKeys(msg tea.KeyPressMsg) (tea.Model, tea.Cmd) {
 		}
 		m.lastFingerprint = "" // force recompute
 		m.lastSplitTaskID = ""
-		m.recomputeAndDisplay(m.visibleSessions())
 		m.viewMode = ViewModeMission
+		m.recomputeAndDisplay(m.visibleSessions())
 		m.mission.SetSize(m.ctx.Width, m.ctx.Height-6)
 	}
 	return m, nil