feat(acadenice): add custom slash commands system for R3.3
Workspace admins can declare dynamic /keyword commands via settings UI
without recompile. Five action types: insert-template, insert-table,
embed-url, run-webhook, insert-snippet. Webhook security: HTTPS-only,
ACADENICE_WEBHOOK_ALLOWLIST allowlist, 10s timeout, no redirects, 1MB cap.
New permission slash_commands:manage added to catalogue (23 perms) and
seeded to Owner + Admin roles.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Corentin
4e2af88144