v0.6.0

refactor(content): share domain services across Web and MCP

Move board, feedback, comment, help center and changelog queries into
scoped domain services while preserving Web and MCP response contracts.
Use explicit projections, UTC dates and precise pagination cursors.

Record successful MCP audits after the business transaction commits so
an audit failure cannot roll back content or invite duplicate writes.

Add cross-transport CRUD, permission, visibility, cursor compatibility,
organization isolation and audit-failure regression coverage.