feat(web+nomos): fix chat streaming reactivity, unified activity timeline, tool cards in chat

- fix(web): Svelte 5 identity-based reactivity broke text_delta streaming —
  immutable message objects in all three chat handlers so text streams live
- feat(web): streaming cursor + inline status indicator merged into message flow
- feat(web): expandable inline tool call cards in chat thread
- feat(web): merge Plan + Event log into one backbone Activity timeline —
  filled status nodes, branch stubs, auto-scroll follow mode, per-session
  activityLog, compact for the rail
- fix(nomos): add X-Accel-Buffering:no to /chat SSE (proxy buffering)
- fix(nomos): plan step auto-close SQL param bug (store.go)
- polish: timestamps, role labels, code copy button, table overflow, min
  window size, delete AgentIndicator/ActivityTimeline dead code

cmd/nomos/main.go

@@ -214,6 +214,7 @@ func handleChat(w http.ResponseWriter, r *http.Request, a *agent, st *store) {
 	w.Header().Set("Content-Type", "text/event-stream")
 	w.Header().Set("Cache-Control", "no-cache")
 	w.Header().Set("Connection", "keep-alive")
+	w.Header().Set("X-Accel-Buffering", "no") // disable proxy buffering
 	w.WriteHeader(200)
 
 	ctx := r.Context()

cmd/nomos/store.go

@@ -1100,9 +1100,9 @@ func (s *store) completeTask(ctx context.Context, sessionID, outcome, summary st
 	}
 	if _, err := s.pool.Exec(ctx, `
 		UPDATE session_plan_steps
-		SET status = $3, finished_at = COALESCE(finished_at, now())
+		SET status = $2, finished_at = COALESCE(finished_at, now())
 		WHERE session_id = $1 AND status IN ('pending', 'running')`,
-		sessionID, "", closeStatus); err != nil {
+		sessionID, closeStatus); err != nil {
 		slog.Warn("nomos: completeTask failed to auto-close in-flight steps", "session", sessionID, "error", err)
 	}