Closes the journal-writer/migration race by running maintenance tasks in the supervisor's main process before any writer child (convey, sense, cortex) is spawned. Migration code moves from convey/maint.py to think/maint.py (clean break, no shim) — convey's startup block and import are removed; sol maint CLI and the --skip-maint flag are unchanged (flag is now a no-op). Phase 2 will add standalone-writer guards so CLIs like sol dream refuse to start without a running supervisor. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>