test: add Operation Lightspeed tests — tab switching, local echo, SSE filters

14 new tests covering tab switch SSE reconnect, terminal buffer edge cases
(tail=0, negative, non-numeric, huge values), extractSessionId filtering,
session lifecycle churn, and concurrent SSE client limits.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Ark0N