Add database persistence to `ReportBoundaryLogs`. On first log for a
session, the handler lazy-creates a `boundary_sessions` row, then
batch-inserts all `BoundaryLog` entries into `boundary_logs`. Structured
logging and usage tracking are preserved. Old boundary clients (no
`session_id`) fall back to log-only mode.
> [!NOTE]
> This PR was authored by Coder Agents.