fix(addie): route engagement ranking queries to admin tool set

[bokelley]

Summary

• Addie wasn't calling list_users_by_engagement because the router had no rule directing engagement/analytics questions to the admin tool set
• The only admin triggers were escalations, org merges, and similar operations
• Added an explicit routing rule for community-wide engagement ranking questions
• Expanded the admin tool set description to include engagement analytics so both signals align

Changes

• server/src/addie/router.ts: Adds routing rule — "Community-wide engagement ranking, most engaged members overall, top contributors, who to invite to events, lifecycle stage analytics → ['admin']"
• server/src/addie/tool-sets.ts: Updates admin tool set description to mention "member insights and engagement analytics, community-wide engagement ranking"

Test plan

• Ask Addie (as an admin) "Who are our most engaged members?" — should now call list_users_by_engagement
• Ask Addie "Who should we invite to the upcoming summit?" — should route to admin and call list_users_by_engagement
• Ask Addie "How engaged is [specific company]?" — should still route to get_account (not affected by this change)
• All existing tests pass (pre-commit hook verifies)

🤖 Generated with Claude Code