rename the TIC system agent to event triage

TIC said nothing about what the agent does, and named the wrong thing: the
tick belongs to the scheduler, which is generic and lives outside it. The
agent's only decision is whether an incoming event deserves an interruption
— it sorts, it never acts — so it is now event-triage, matching the
functional naming of the two memory lints.

- agents/tic/ -> agents/event-triage/, module tic/ -> event_triage/,
  TicManager -> EventTriageManager, TicConfig -> EventTriageConfig
- agent id and chat source: "tic" -> "event-triage"
- config keys: tic.* -> event_triage.*, and the config.yml section tic: ->
  event_triage: (greenfield: previously set values fall back to defaults)
- i18n en/it/fr: Event triage / Triage eventi / Tri des evenements; dropped
  the stale "TIC sessions" mention from the debug-pages description
- docs/system-agents.md, docs/index.md, docs/settings.md, CLAUDE.md, SKALD.md

src/frontend/api/sessions.rs

@@ -593,7 +593,7 @@ fn build_items<'a>(
             let failed = msg.status == "failed";
             match msg.role {
                 chat_history::Role::User => {
-                    // Skip synthetic messages (TIC notifications, etc.) — they are
+                    // Skip synthetic messages (event triage notifications, etc.) — they are
                     // injected as user turns for the LLM but must not appear in the UI.
                     if msg.is_synthetic {
                         continue;