RaidLead

v1.9.1: Ask Missing - chase only the players still lacking a role

A role check that ends with two or three people still "unknown" forced a
full re-poll of the entire raid. Ask Missing targets just those players:
peers running RaidLead get the role popup via a targeted whisper (nobody
else is disturbed), everyone else gets a plain whisper they can answer
with a number. Replies are read exactly as in a normal role check.

- Modules/Roles.lua: GetMissingRolePlayers() (skips offline players and
  self), AskMissingRoles(), and a paced whisper pump - firing
  SendChatMessage in a loop for a dozen players trips the server's chat
  flood protection.
- Modules/Roles.lua: extract ActivateListening() with a generation
  counter, shared by both entry points. Fixes a latent bug where starting
  a second role check left the first one's 90s auto-stop timer armed, so
  it would cut the new check short.
- UI/HealAssignFrame.lua: Ask Missing button showing the outstanding
  count, with a tooltip listing exactly who is still missing. Roster
  header labels shortened to fit: Request Role Check -> Role Check,
  Ask Roles (chat) -> Ask All.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>