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

crates/skald-core/src/chat_hub/inbox.rs

@@ -44,7 +44,7 @@ pub(super) struct SourceInbox {
 /// consumer to seed a turn. No coalescing: any further queued messages are drained
 /// into the running turn at its round boundaries (see `drain_leading_user`).
 ///
-/// Empty queue → `None`. Synthetic messages (notification/TIC) and plain user
+/// Empty queue → `None`. Synthetic messages (notification/event triage) and plain user
 /// messages are treated identically here; only `drain_leading_user` distinguishes
 /// them, leaving synthetic ones for the notification path.
 pub(super) fn build_unit(