Group-scoped agents could read sessions from other groups via session
tools (sessions_list, sessions_history, session_status, sessions_send)
because they only checked agent_key, not group context. This caused
cron jobs to leak data from unrelated groups into reports.
Add isSessionInScope() guard to all 4 session tools with colon-bounded
chatID matching. New share_sessions setting (default false) controls
cross-group visibility, following the same pattern as share_memory and
share_knowledge_graph. Web UI toggle and i18n strings included.
63 test cases covering guild/DM/group users, realistic Zalo IDs,
boundary exactness, multi-colon chatIDs, and the exact bug scenario.